2022-03-12 11:26:00

13 files changed, 2168 insertions, 262 deletions

diff --git a/doc/context/documents/general/manuals/luametatex.pdf b/doc/context/documents/general/manuals/luametatex.pdf
index 123c3f000..224d64fd1 100644
--- a/doc/context/documents/general/manuals/luametatex.pdf
+++ b/doc/context/documents/general/manuals/luametatex.pdf
diff --git a/doc/context/documents/general/manuals/ontarget.pdf b/doc/context/documents/general/manuals/ontarget.pdf
index c4d0077e4..e4fb54bc4 100644
--- a/doc/context/documents/general/manuals/ontarget.pdf
+++ b/doc/context/documents/general/manuals/ontarget.pdf
diff --git a/doc/context/sources/general/manuals/luametatex/luametatex-differences.tex b/doc/context/sources/general/manuals/luametatex/luametatex-differences.tex
index 3e80f4ae5..3da557f40 100644
--- a/doc/context/sources/general/manuals/luametatex/luametatex-differences.tex
+++ b/doc/context/sources/general/manuals/luametatex/luametatex-differences.tex
@@ -95,6 +95,15 @@ This chapter will discuss what is gone. We start with the primitives that were d
                 \NC \NR
 \stoptabulate
 
+The math machinery has been overhauled stepwise. In the process detailed control
+has been added but later some of that got removed or replaced. The engine now
+assumes that \OPENTYPE\ fonts are used but you do need to set up the engine
+properly, something that has to be done with respect to fonts anyway. By enabling
+and|/|disabling certain features you can emulate the traditional engine. Font
+parameters no longer are taken from the traditional parameters when they are not
+set. We just assume properly passed so called math constants and quite a few new
+ones have been added.
+
 The resources and positioning primitives are actually useful but can be defined
 as macros that (via \LUA) inject nodes in the input that suit the macro package
 and backend. The three||letter direction primitives are gone and the numeric
@@ -102,7 +111,7 @@ variants are now leading. There is no need for page and body related directions
 and they don't work well in \LUATEX\ anyway. We only have two directions left.
 Because we can hook in \LUA\ functions that get information about what is expected
 (consumer or provider) there are plenty possibilities for adding functionality
-using this scripting langauge.
+using this scripting language.
 
 The primitive related extensions were not that useful and reliable so they have
 been removed. There are some new variants that will be discussed later. The \type
@@ -368,7 +377,8 @@ back mapping if needed (just alias the functions).
 It's all part of trying to make the code base consistent but it is sometimes a
 bit annoying. However, that's why we develop this engine independent of the
 \LUATEX\ code base. It's anyway a change that has been on my todo list for quite
-a while because those inconsistencies annoyed me.
+a while because those inconsistencies annoyed me. It might take some years to
+get all done.
 
 \stopchapter
 
diff --git a/doc/context/sources/general/manuals/luametatex/luametatex-fonts.tex b/doc/context/sources/general/manuals/luametatex/luametatex-fonts.tex
index 5f0ea780a..1c2670ff4 100644
--- a/doc/context/sources/general/manuals/luametatex/luametatex-fonts.tex
+++ b/doc/context/sources/general/manuals/luametatex/luametatex-fonts.tex
@@ -120,9 +120,9 @@ has no ligatures and kerns and is normally not processed at all.
 \NC \type {rightprotruding} \NC number  \NC right protruding factor (\prm {rpcode}) \NC\NR
 \NC \type {expansion}       \NC number  \NC expansion factor (\prm {efcode}) \NC\NR
 \NC \type {next}            \NC number  \NC \quote {next larger} character index \NC\NR
-\NC \type {extensible}      \NC table   \NC constituent parts of an extensible recipe \NC\NR
-\NC \type {vvariants}       \NC table   \NC constituent parts of a vertical variant set \NC \NR
-\NC \type {hvariants}       \NC table   \NC constituent parts of a horizontal variant set \NC \NR
+\NC \type {extensible}      \NC table   \NC constituent parts of an extensible (traditional) recipe \NC\NR
+\NC \type {vparts}          \NC table   \NC constituent parts of a vertical (\OPENTYPE) recipe \NC \NR
+\NC \type {hparts}          \NC table   \NC constituent parts of a horizontal (\OPENTYPE)recipe \NC \NR
 \NC \type {kerns}           \NC table   \NC kerning information \NC\NR
 \NC \type {ligatures}       \NC table   \NC ligaturing information \NC\NR
 \NC \type {mathkern}        \NC table   \NC math cut-in specifications \NC\NR
@@ -169,7 +169,7 @@ well as on the value of \prm {adjustspacing}.
 A math character can have a \type {next} field that points to a next larger
 shape. However, the presence of \type {extensible} will overrule \type {next}, if
 that is also present. The \type {extensible} field in turn can be overruled by
-\type {vvariants}, the \OPENTYPE\ version. The \type {extensible} table is very
+\type {vparts}, the \OPENTYPE\ version. The \type {extensible} table is very
 simple:
 
 \starttabulate[|l|l|p|]
@@ -182,7 +182,7 @@ simple:
 \LL
 \stoptabulate
 
-The \type {hvariants} and \type {vvariants} are arrays of components. Each of
+The \type {hparts} and \type {vparts} are arrays of components. Each of
 those components is itself a hash of up to five keys:
 
 \starttabulate[|l|l|p|]
diff --git a/doc/context/sources/general/manuals/luametatex/luametatex-math.tex b/doc/context/sources/general/manuals/luametatex/luametatex-math.tex
index 30ce11c3b..eb3f6c61d 100644
--- a/doc/context/sources/general/manuals/luametatex/luametatex-math.tex
+++ b/doc/context/sources/general/manuals/luametatex/luametatex-math.tex
@@ -10,6 +10,9 @@
 
 \topicindex {math}
 
+End 2021 this chapter started with this:
+
+\startquotation
 At this point there is no difference between \LUAMETATEX\ and \LUATEX\ with
 respect to math. \footnote {This might no longer be true because we have more
 control options that define default behavior and also have a more extensive
@@ -30,6 +33,24 @@ than gradually add more and more. At some point we should be able to say \quote
 {This is it}. Also, when looking at these features, you need to keep in mind that
 when it comes to math, \LATEX\ is the dominant macro package and it never needed
 these engine features, so most are probably just here for exploration purposes.
+\stopquotation
+
+Although we still process math as \TEX\ does, there have been some fundamental
+changes to the machinery. Most of that is discussed in documents that come with
+\CONTEXT\ and in Mikael Sundqvist math manual. Together we explored some new ways
+to deal with math spacing, penalties, fencing, operators, fractions, atoms and
+other features of the \TEX\ engine. We started from the way \CONTEXT\ used the
+already present functionality combine with sometimes somewhat dirty (but on the
+average working well) tricks.
+
+It will take a while before this chapter is updated. If you find errors or things
+missing, let me know. A lot of pairwise spacing primitives were dropped but also
+quite a bit of new ones introduced to control matters. Much in \LUAMETATEX\ math
+handling is about micro|-|typography and for us the results are quite visible.
+But, as far as we know, there have never been complaints or demands in the
+direction of the features discussed here. Also, \TEX\ math usage outside
+\CONTEXT\ is rather chiselled in stone (already for nearly three decades) so we
+don't expect other macro packages to use the new features anyway.
 
 \stopsection
 
@@ -38,18 +59,19 @@ these engine features, so most are probably just here for exploration purposes.
 \topicindex {math+\UNICODE}
 \topicindex {\UNICODE+math}
 
-Character handling is now extended up to the full \UNICODE\ range (the \type {\U}
-prefix), which is compatible with \XETEX.
+For various reasons we need to encode a math character in a 32 bit number and
+because we often also need to keep track of families and classes the range of
+characters is limited to 20 bits. There are upto 64 classes (more than in
+\LUATEX) and 64 families (less than in \LUATEX). The upper limit of characters is
+less that what \UNICODE\ offers but for math we're okay. If needed we can provide
+less families.
 
 The math primitives from \TEX\ are kept as they are, except for the ones that
 convert from input to math commands: \type {mathcode}, and \type {delcode}. These
-two now allow for a 21-bit character argument on the left hand side of the equals
-sign.
-
-Some of the new \LUATEX\ primitives read more than one separate value. This is
-shown in the tables below by a plus sign.
-
-The input for such primitives would look like this:
+two now allow for the larger character codes argument on the left hand side of
+the equals sign. The number variants of some primitives might be dropped in favor
+of the primitives that read more than one separate value (class, family and
+code), for instance:
 
 \starttyping
 \def\overbrace{\Umathaccent 0 1 "23DE }
@@ -78,70 +100,128 @@ The unaltered ones are:
 \LL
 \stoptabulate
 
-For practical reasons \prm {mathchardef} will silently accept values larger
-that \type {0x8000} and interpret it as \prm {Umathcharnumdef}. This is needed
-to satisfy older macro packages.
-
-The following new primitives are compatible with \XETEX:
-
-% somewhat fuzzy:
+In \LUATEX\ we support the single number primitives *with \type {num} in their
+name) conforming the \XETEX\ method. For the moment that still works but you need
+to figure out the number yourself. The split number variants are more future safe
+with respect to classes and families. Wd don't document \prm {Umathcharnumdef},
+\prm {Umathcharnum}, \prm {Umathcodenum} and \prm {Udelcodenum} here any longer.
 
-\starttabulate[|l|l|r|c|l|r|]
-\DB primitive                             \BC min       \BC max         \BC \kern 2em \BC min       \BC max         \NC \NR
+\starttabulate[|l|l|c|c|c|]
+\DB primitive           \BC        \BC class \BC family \BC character \NC \NR
 \TB
-\NC \prm {Umathchardef}                   \NC 0+0+0     \NC 7+FF+10FFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Umathcharnumdef}\rlap{\high{5}} \NC -80000000 \NC    7FFFFFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Umathcode}                      \NC 0         \NC      10FFFF \NC =         \NC 0+0+0     \NC 7+FF+10FFFF \NC \NR
-\NC \prm {Udelcode}                       \NC 0         \NC      10FFFF \NC =         \NC 0+0       \NC   FF+10FFFF \NC \NR
-\NC \prm {Umathchar}                      \NC 0+0+0     \NC 7+FF+10FFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Umathaccent}                    \NC 0+0+0     \NC 7+FF+10FFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Udelimiter}                     \NC 0+0+0     \NC 7+FF+10FFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Uradical}                       \NC 0+0       \NC   FF+10FFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Umathcharnum}                   \NC -80000000 \NC    7FFFFFFF \NC           \NC           \NC             \NC \NR
-\NC \prm {Umathcodenum}                   \NC 0         \NC      10FFFF \NC =         \NC -80000000 \NC    7FFFFFFF \NC \NR
-\NC \prm {Udelcodenum}                    \NC 0         \NC      10FFFF \NC =         \NC -80000000 \NC    7FFFFFFF \NC \NR
+\NC \prm {Umathchardef} \NC csname \NC "40   \NC "40    \NC "FFFFF     \NC \NR
+\NC \prm {Umathcode}    \NC        \NC "40   \NC "40    \NC "FFFFF     \NC \NR
+\NC \prm {Udelcode}     \NC "FFFFF \NC "40   \NC "40    \NC "FFFFF     \NC \NR
+\NC \prm {Umathchar}    \NC        \NC "40   \NC "40    \NC "FFFFF     \NC \NR
+\NC \prm {Umathaccent}  \NC        \NC "40   \NC "40    \NC "FFFFF     \NC \NR
+\NC \prm {Udelimiter}   \NC        \NC "40   \NC "40    \NC "FFFFF     \NC \NR
+\NC \prm {Uradical}     \NC        \NC "40   \NC "40    \NC "FFFFF     \NC \NR
 \LL
 \stoptabulate
 
-Specifications typically look like:
+So, there are upto 64 classes of which at this moment about 20 are predefined so,
+taking some future usage by the engine into account,you can assume 32 upto 63 to
+be available for any purpose. The number of families has been reduced from 256 to
+64 which is plenty for daily use in an \OPENTYPE\ setup. If we ever need to
+expand the \UNICODE\ range there will be less families. The values of begin and
+end classes and the number of classes can be fetched from the \LUA\ status
+table.
+
+Given the above, specifications typically look like:
 
 \starttyping
-\Umathchardef\xx="1"0"456
-\Umathcode   123="1"0"789
+\Umathchardef \xx = "1 "0 "456
+\Umathcode    123 = "1 "0 "789
 \stoptyping
 
 The new primitives that deal with delimiter|-|style objects do not set up a
 \quote {large family}. Selecting a suitable size for display purposes is expected
-to be dealt with by the font via the \prm {Umathoperatorsize} parameter.
-
-For some of these primitives, all information is packed into a single signed
-integer. For the first two (\prm {Umathcharnum} and \prm {Umathcodenum}), the
-lowest 21 bits are the character code, the 3 bits above that represent the math
-class, and the family data is kept in the topmost bits. This means that the values
-for math families 128--255 are actually negative. For \prm {Udelcodenum} there
-is no math class. The math family information is stored in the bits directly on
-top of the character code. Using these three commands is not as natural as using
-the two- and three|-|value commands, so unless you know exactly what you are
-doing and absolutely require the speedup resulting from the faster input
-scanning, it is better to use the verbose commands instead.
+to be dealt with by the font via the \prm {Umathoperatorsize} parameter. Old
+school fonts can still be handled but you need to set up the engine to do that;
+this can be done per font. In principle we assume that \OPENTYPE\ fonts are used,
+which is no big deal because loading fonts is already under \LUA\ control. At
+that moment the distinction between small and large delimiters will be gone. Of
+course an alternative is to support a specific large size but that is unlikely to
+happen.
+
+% For some of these primitives, all information is packed into a single signed
+% integer. For the first two (\prm {Umathcharnum} and \prm {Umathcodenum}), the
+% lowest 21 bits are the character code, the 3 bits above that represent the math
+% class, and the family data is kept in the topmost bits. This means that the values
+% for math families 128--255 are actually negative. For \prm {Udelcodenum} there
+% is no math class. The math family information is stored in the bits directly on
+% top of the character code. Using these three commands is not as natural as using
+% the two- and three|-|value commands, so unless you know exactly what you are
+% doing and absolutely require the speedup resulting from the faster input
+% scanning, it is better to use the verbose commands instead.
 
 The \prm {Umathaccent} command accepts optional keywords to control various
 details regarding math accents. See \in {section} [mathacc] below for details.
 
 There are more new primitives and all of these will be explained in following
-sections:
+sections. For instance these are variants of radicals and delimiters all are
+set the same::
 
-\starttabulate[|l|l|]
-\DB primitive                \BC value range (in hex) \NC \NR
+\starttabulate[|l|c|c|c|]
+\DB primitive              \BC class \BC family \NC character \NC \NR
+\TB
+\NC \prm {Uroot}           \NC "40   \NC "40    \NC "FFFFF    \NC \NR
+\NC \prm {Uoverdelimiter}  \NC "40   \NC "40    \NC "FFFFF    \NC \NR
+\NC \prm {Uunderdelimiter} \NC "40   \NC "40    \NC "FFFFF    \NC \NR
+\NC \prm {Udelimiterover}  \NC "40   \NC "40    \NC "FFFFF    \NC \NR
+\NC \prm {Udelimiterunder} \NC "40   \NC "40    \NC "FFFFF    \NC \NR
+\LL
+\stoptabulate
+
+In addition there are \prm {UVextensible} and \prm {Uoperator} and extended
+versions of fenced: \prm {Uleft}, \prm {Uright} and \prm {Umiddle}. There is also
+\prm {Uover} and similar primitives that expect the numerator and denominator
+after the primitive. In addition to regular scripts there are prescripts and a
+dedicated prime script. Many of these \type {U} primitives can be controlled by
+options and keywords.
+
+\stopsection
+
+\startsection[title=Setting up the engine]
+
+\topicindex{math+control}
+
+Processing math is controlled by \prm {mathfontcontrol}, a numeric bitset
+parameter. The recommended bits are marked with a star but it really depends on
+the macro package to set up the machinery well. Of course one can just enable all
+and see what happens.
+
+\starttabulate[|l|l|c|]
+\DB bit             \BC name                            \NC \NC \NR
 \TB
-\NC \prm {Uroot}           \NC 0 + 0--FF + 10FFFF   \NC \NR
-\NC \prm {Uoverdelimiter}  \NC 0 + 0--FF + 10FFFF   \NC \NR
-\NC \prm {Uunderdelimiter} \NC 0 + 0--FF + 10FFFF   \NC \NR
-\NC \prm {Udelimiterover}  \NC 0 + 0--FF + 10FFFF   \NC \NR
-\NC \prm {Udelimiterunder} \NC 0 + 0--FF + 10FFFF   \NC \NR
+\NC \type {0x00001} \NC \type {usefontcontrol}          \NC \star \NR
+\NC \type {0x00002} \NC \type {overrule}                \NC \star \NR
+\NC \type {0x00004} \NC \type {underrule}               \NC \star \NR
+\NC \type {0x00008} \NC \type {radicalrule}             \NC \star \NR
+\NC \type {0x00010} \NC \type {fractionrule}            \NC \star \NR
+\NC \type {0x00020} \NC \type {accentskewhalf}          \NC \star \NR
+\NC \type {0x00040} \NC \type {accentskewapply}         \NC \star \NR
+\NC \type {0x00080} \NC \type {checkligatureandkern}    \NC       \NR
+\NC \type {0x00100} \NC \type {applyverticalitalickern} \NC \star \NR
+\NC \type {0x00200} \NC \type {applyordinaryitalickern} \NC \star \NR
+\NC \type {0x00400} \NC \type {applycharitalickern}     \NC       \NR
+\NC \type {0x00800} \NC \type {reboxcharitalickern}     \NC       \NR
+\NC \type {0x01000} \NC \type {applyboxeditalickern}    \NC \star \NR
+\NC \type {0x02000} \NC \type {staircasekern}           \NC \star \NR
+\NC \type {0x04000} \NC \type {applytextitalickern}     \NC \star \NR
+\NC \type {0x08000} \NC \type {checktextitalickern}     \NC \star \NR
+\NC \type {0x10000} \NC \type {checkspaceitalickern}    \NC       \NR
+\NC \type {0x20000} \NC \type {applyscriptitalickern}   \NC \star \NR
+\NC \type {0x40000} \NC \type {italicshapekern}         \NC \star \NR
 \LL
 \stoptabulate
 
+One reason for this approach is that traditional and \OPENTYPE\ fonts have
+different approaches (especially when it comes to dealing with the width and
+italic corrections) and is even more complicated by the fact that the fonts are
+often inconsistent (within and between). In \CONTEXT\ we deal with this by
+runtime fixes to fonts. In any case the Cambria font is taken as reference.
+
 \stopsection
 
 \startsection[title={Math styles}]
@@ -346,8 +426,8 @@ we force styles in the script using \prm {scriptstyle} and \prm
 Now we set the following parameters
 
 \startbuffer[setup]
-\Umathordrelspacing\scriptstyle=30mu
-\Umathordordspacing\scriptstyle=30mu
+\setmathspacing 0 3 \scriptstyle = 30mu
+\setmathspacing 0 3 \scriptstyle = 30mu
 \stopbuffer
 
 \typebuffer[setup]
@@ -359,10 +439,10 @@ This gives a different result:
 But, as this is not what is expected (visually) we should say:
 
 \startbuffer[setup]
-\Umathordrelspacing\scriptstyle=30mu
-\Umathordordspacing\scriptstyle=30mu
-\Umathordrelspacing\crampedscriptstyle=30mu
-\Umathordordspacing\crampedscriptstyle=30mu
+\setmathspacing 0 3 \scriptstyle        = 30mu
+\setmathspacing 0 3 \scriptstyle        = 30mu
+\setmathspacing 0 3 \crampedscriptstyle = 30mu
+\setmathspacing 0 3 \crampedscriptstyle = 30mu
 \stopbuffer
 
 \typebuffer[setup]
@@ -386,7 +466,7 @@ now accessible via primitive commands. In fact, refactoring of the math engine
 has resulted in turning some hard codes properties into parameters.
 
 \starttabulate
-\DB primitive name                   \BC description \NC \NR
+\DB primitive name                 \BC description \NC \NR
 \TB
 \NC \prm {Umathquad}               \NC the width of 18 mu's \NC \NR
 \NC \prm {Umathaxis}               \NC height of the vertical center axis of
@@ -441,12 +521,39 @@ has resulted in turning some hard codes properties into parameters.
 \NC \prm {Umathsupsubbottommax}    \NC the bottom of the superscript of a combined super- and subscript
                                        be at least as high as this above the baseline \NC \NR
 \NC \prm {Umathsubsupvgap}         \NC vertical clearance between super- and subscript \NC \NR
-\NC \prm {Umathspacebeforescript}  \NC additional space added before a super- or subprescript (bonus setting) \NC \NR
 \NC \prm {Umathspaceafterscript}   \NC additional space added after a super- or subscript \NC \NR
 \NC \prm {Umathconnectoroverlapmin}\NC minimum overlap between parts in an extensible recipe \NC \NR
 \LL
 \stoptabulate
 
+In addition to the above official \OPENTYPE\ font parameters we have these:
+
+\starttabulate
+\DB primitive name                            \BC description \NC \NR
+\TB
+\NC \prm{Umathprimeraisepercent}              \NC the percentage that the vertical position is scaled \NC \NR
+\NC \prm{Umathprimeshiftup}                   \NC the prime variant of \prm {SuperscriptShiftUp} \NC \NR
+\NC \prm{Umathprimebaselinedropmax}           \NC the prime variant of \prm {SuperscriptBaselineDropMax} \NC \NR
+\NC \prm{Umathprimeshiftupcramped}            \NC the prime variant of \prm {SuperscriptShiftUpCramped} \NC \NR
+\NC \prm{Umathprimespaceafter}                \NC the prime variant of \prm {UmathSpaceAfterScript} \NC \NR
+\NC \prm{Umathprimewidthpercent}              \NC the percentage of width that gets added \NC \NR
+\NC \prm{Umathspacebeforescript}              \NC the prescript variant of \prm {UmathSpaceAfterScript} \NC \NR
+\NC \prm{Umathnolimitsupfactor}               \NC a multiplier for the way limits are shifted up and down \NC \NR
+\NC \prm{Umathnolimitsubfactor}               \NC a multiplier for the way limits are shifted up and down \NC \NR
+\NC \prm{Umathaccenttopshiftup}               \NC the amount that a top accent is shifted up \NC \NR
+\NC \prm{Umathaccentbottomshiftdown}          \NC the amount that a bottom accent is shifted down \NC \NR
+\NC \prm{Umathflattenedaccenttopshiftup}      \NC the amount that a wide top accent is shifted up \NC \NR
+\NC \prm{Umathflattenedaccentbottomshiftdown} \NC the amount that a wide bottom accent is shifted down \NC \NR
+\NC \prm{Umathaccentbasedepth}                \NC the complement of \prm {UmathAccentBaseHeight} \NC \NR
+\NC \prm{Umathaccentflattenedbasedepth}       \NC the complement of \prm {UmathFlattenedAccentBaseHeight} \NC \NR
+\LL
+\stoptabulate
+
+These parameters not only provide a bit more control over rendering, they also
+can be used in compensating issues in font, because no font is perfect. Some are
+the side effects of experiments and they have CamelCase companions in the \type
+{MathConstants} table.
+
 Each of the parameters in this section can be set by a command like this:
 
 \starttyping
@@ -456,6 +563,26 @@ Each of the parameters in this section can be set by a command like this:
 they obey grouping, and you can use \type {\the\Umathquad\displaystyle} if
 needed.
 
+There are quite some parameters that can be set and there are eight styles, which means a lot
+of keying in. For that reason is is possible to set parameters groupwise
+
+\starttabulate
+\DB primitive name               \BC description \NC \NR
+\TB
+\NC \prm {alldisplaystyles}      \NC set both display styles \NC \NR
+\NC \prm {alltextstyles}         \NC set both text styles \NC \NR
+\NC \prm {allscriptstyles}       \NC set both script styles \NC \NR
+\NC \prm {allscriptscriptstyles} \NC set both scriptscript styles \NC \NR
+\NC \prm {allmathstyles}         \NC set all eight styles \NC \NR
+\NC \prm {allsplitstyles}        \NC set all display and text styles, and reset all script(script) styles \NC \NR
+\NC \prm {alluncrampedstyles}    \NC set all four uncramped styles \NC \NR
+\NC \prm {allcrampedstyles}      \NC set all four cramped styles \NC \NR
+\LL
+\stoptabulate
+
+These groups are especially handy when you set up inter atom spacing, pre- and
+post atom penalties and atom rules.
+
 \stopsubsection
 
 \startsubsection[title={Font|-|based math parameters}]
@@ -552,6 +679,8 @@ dimension parameter. For math fonts, this should be set to zero.
 \LL
 \stoptabulate
 
+{\em Todo: add the extra ones.}
+
 Note 1: \OPENTYPE\ fonts set \prm {Umathlimitabovekern} and \prm
 {Umathlimitbelowkern} to zero and set \prm {Umathquad} to the font size of the
 used font, because these are not supported in the \type {MATH} table,
@@ -660,104 +789,51 @@ applicable in the first occasion that checks them (linebreaking or packaging).
 
 \stopsubsection
 
-\startsubsection[title={Pairwise spacing and \tex {Umath...spacing} commands}]
+\startsubsection[title={Pairwise spacing}]
 
 \topicindex {math+spacing}
 
-Besides the parameters mentioned in the previous sections, there are also 64 new
+Besides the parameters mentioned in the previous sections, there are also
 primitives to control the math spacing table (as explained in Chapter~18 of the
-\TEX book). The primitive names are a simple matter of combining two math atom
-types, but for completeness' sake, here is the whole list:
+\TEX book). This happens per class pair. Because we have many possible classes,
+we no longer hand the many primitives that \LUATEX\ has but you can define then
+using the generic \prm {setmathspacing} primitive:
 
-\starttwocolumns
-\startlines
-\prm {Umathordordspacing}
-\prm {Umathordopspacing}
-\prm {Umathordbinspacing}
-\prm {Umathordrelspacing}
-\prm {Umathordopenspacing}
-\prm {Umathordclosespacing}
-\prm {Umathordpunctspacing}
-\prm {Umathordinnerspacing}
-\prm {Umathopordspacing}
-\prm {Umathopopspacing}
-\prm {Umathopbinspacing}
-\prm {Umathoprelspacing}
-\prm {Umathopopenspacing}
-\prm {Umathopclosespacing}
-\prm {Umathoppunctspacing}
-\prm {Umathopinnerspacing}
-\prm {Umathbinordspacing}
-\prm {Umathbinopspacing}
-\prm {Umathbinbinspacing}
-\prm {Umathbinrelspacing}
-\prm {Umathbinopenspacing}
-\prm {Umathbinclosespacing}
-\prm {Umathbinpunctspacing}
-\prm {Umathbininnerspacing}
-\prm {Umathrelordspacing}
-\prm {Umathrelopspacing}
-\prm {Umathrelbinspacing}
-\prm {Umathrelrelspacing}
-\prm {Umathrelopenspacing}
-\prm {Umathrelclosespacing}
-\prm {Umathrelpunctspacing}
-\prm {Umathrelinnerspacing}
-\prm {Umathopenordspacing}
-\prm {Umathopenopspacing}
-\prm {Umathopenbinspacing}
-\prm {Umathopenrelspacing}
-\prm {Umathopenopenspacing}
-\prm {Umathopenclosespacing}
-\prm {Umathopenpunctspacing}
-\prm {Umathopeninnerspacing}
-\prm {Umathcloseordspacing}
-\prm {Umathcloseopspacing}
-\prm {Umathclosebinspacing}
-\prm {Umathcloserelspacing}
-\prm {Umathcloseopenspacing}
-\prm {Umathcloseclosespacing}
-\prm {Umathclosepunctspacing}
-\prm {Umathcloseinnerspacing}
-\prm {Umathpunctordspacing}
-\prm {Umathpunctopspacing}
-\prm {Umathpunctbinspacing}
-\prm {Umathpunctrelspacing}
-\prm {Umathpunctopenspacing}
-\prm {Umathpunctclosespacing}
-\prm {Umathpunctpunctspacing}
-\prm {Umathpunctinnerspacing}
-\prm {Umathinnerordspacing}
-\prm {Umathinneropspacing}
-\prm {Umathinnerbinspacing}
-\prm {Umathinnerrelspacing}
-\prm {Umathinneropenspacing}
-\prm {Umathinnerclosespacing}
-\prm {Umathinnerpunctspacing}
-\prm {Umathinnerinnerspacing}
-\stoplines
-\stoptwocolumns
+\starttyping
+\def\Umathordordspacing     {\setmathspacing 0 0 }
+\def\Umathordordopenspacing {\setmathspacing 0 4 }
+\stoptyping
 
 These parameters are of type \prm {muskip}, so setting a parameter can be done
 like this:
 
 \starttyping
-\Umathopordspacing\displaystyle=4mu plus 2mu
+\setmathspacing 1 0 \displaystyle=4mu plus 2mu % op ord Umathopordspacing
 \stoptyping
 
-They are all initialized by \type {initex} to the values mentioned in the table
-in Chapter~18 of the \TEX book.
+The atom pairs known by the engine are all initialized by \type {initex} to the
+values mentioned in the table in Chapter~18 of the \TEX book.
+
+For ease of use as well as for backward compatibility, \prm {thinmuskip}, \prm
+{medmuskip} and \prm {thickmuskip} are treated specially. In their case a pointer
+to the corresponding internal parameter is saved, not the actual \prm {muskip}
+value. This means that any later changes to one of these three parameters will be
+taken into account. As a bonus we also introduced a \prm {tinymuskip} primitive.
 
-Note 1: For ease of use as well as for backward compatibility, \prm {thinmuskip},
-\prm {medmuskip} and \prm {thickmuskip} are treated specially. In their case a
-pointer to the corresponding internal parameter is saved, not the actual \prm
-{muskip} value. This means that any later changes to one of these three
-parameters will be taken into account.
+In \LUAMETATEX\ we go a bit further. Any named dimension, glue and mu glue
+register as well as the constants with these properties can be bound to a pair by
+prefixing \prm {setmathspacing} by \prm {inherited}.
 
-Note 2: Careful readers will realise that there are also primitives for the items
-marked \type {*} in the \TEX book. These will not actually be used as those
-combinations of atoms cannot actually happen, but it seemed better not to break
-orthogonality. They are initialized to zero.
+Careful readers will realize that there are also primitives for the items marked
+\type {*} in the \TEX book. These will actually be used because we pose no
+restrictions. However, you can enforce the remapping rules to conform to the
+rules of \TEX\ (or yourself).
+
+{\em Todo: explain rules.}
+
+{\em Todo: explain penalties.}
+
+{\em Todo: explain let, set and copy primitives.}
 
 \stopsubsection
 
@@ -1413,8 +1489,8 @@ where the options can be \type {noaxis} and \type {exact}. By default we add hal
 the axis to the shifts and by default we zero the width of the middle character.
 For Latin Modern the result looks as follows:
 
-\def\ShowA#1#2#3{$x + { {#1} \Uskewed           /    #3 {#2} } + x$}
-\def\ShowB#1#2#3{$x + { {#1} \Uskewedwithdelims / () #3 {#2} } + x$}
+\def\ShowA#1#2#3{$x + { \Uskewed           /    #3 {#1} {#2} } + x$}
+\def\ShowB#1#2#3{$x + { \Uskewedwithdelims / () #3 {#1} {#2} } + x$}
 
 \start
     \switchtobodyfont[modern]
@@ -1659,7 +1735,7 @@ and \prm {Usubscript}}]
 \type {^}, \type {_}, \type {$}, and \type {$$}:
 
 \starttabulate[|l|l|]
-\DB primitive                  \BC explanation \NC \NR
+\DB primitive                \BC explanation \NC \NR
 \TB
 \NC \prm {Usuperscript}      \NC duplicates the functionality of \type {^} \NC \NR
 \NC \prm {Usubscript}        \NC duplicates the functionality of \type {_} \NC \NR
@@ -1703,85 +1779,12 @@ results in \inlinebuffer[script].
 
 \stopsubsection
 
-\startsubsection[title={Allowed math commands in non|-|math modes}]
-
-\topicindex {math+text}
-\topicindex {text+math}
-
-The commands \prm {mathchar}, and \prm {Umathchar} and control sequences that are
-the result of \prm {mathchardef} or \prm {Umathchardef} are also acceptable in
-the horizontal and vertical modes. In those cases, the \prm {textfont} from the
-requested math family is used.
-
-\stopsubsection
-
-\stopsection
-
-\startsection[title={Goodies}]
-
-\startsubsection[title={Flattening: \prm {mathflattenmode}}]
-
-\topicindex {math+flattening}
-
-The \TEX\ math engine collapses \type {ord} noads without sub- and superscripts
-and a character as nucleus, which has the side effect that in \OPENTYPE\ mode
-italic corrections are applied (given that they are enabled).
-
-\startbuffer[sample]
-\switchtobodyfont[modern]
-$V \mathbin{\mathbin{v}} V$\par
-$V \mathord{\mathord{v}} V$\par
-\stopbuffer
-
-\typebuffer[sample]
-
-This renders as:
-
-\blank \start \mathflattenmode\plusone \getbuffer[sample] \stop \blank
-
-When we set \prm {mathflattenmode} to 31 we get:
-
-\blank \start \mathflattenmode\numexpr1+2+4+8+16\relax \getbuffer[sample] \stop \blank
-
-When you see no difference, then the font probably has the proper character
-dimensions and no italic correction is needed. For Latin Modern (at least till
-2018) there was a visual difference. In that respect this parameter is not always
-needed unless of course you want efficient math lists anyway.
-
-You can influence flattening by adding the appropriate number to the value of the
-mode parameter. The default value is~1.
-
-\starttabulate[|Tc|c|]
-\DB mode \BC class \NC \NR
-\TB
-\NC  1   \NC ord   \NC \NR
-\NC  2   \NC bin   \NC \NR
-\NC  4   \NC rel   \NC \NR
-\NC  8   \NC punct \NC \NR
-\NC 16   \NC inner \NC \NR
-\LL
-\stoptabulate
-
-\stopsubsection
-
-\startsubsection[title={Less Tracing}]
+\startsubsection[title={Injecting primes with {Uprimescript}}]
 
-\topicindex {math+tracing}
-
-Because there are quite some math related parameters and values, it is possible
-to limit tracing. Only when \type {tracingassigns} and|/|or \type
-{tracingrestores} are set to~2 or more they will be traced.
+{\em Todo: explain this one.}
 
 \stopsubsection
 
-\stopsection
-
-\startsection[title={Experiments}]
-
-There are a couple of experimental features. They will stay but details might
-change, for instance more control over spacing. We just show some examples and
-let your imagination work it out. First we have prescripts:
-
 \startsubsection[title={Prescripts with \prm {Usuperprescript} and {Usubprescript}}]
 
 \startbuffer
@@ -1829,6 +1832,85 @@ These more verbose triggers can be used to build interfaces:
 
 \stopsubsection
 
+\startsubsection[title={Allowed math commands in non|-|math modes}]
+
+\topicindex {math+text}
+\topicindex {text+math}
+
+The commands \prm {mathchar}, and \prm {Umathchar} and control sequences that are
+the result of \prm {mathchardef} or \prm {Umathchardef} are also acceptable in
+the horizontal and vertical modes. In those cases, the \prm {textfont} from the
+requested math family is used.
+
+\stopsubsection
+
+\stopsection
+
+\startsection[title={Goodies}]
+
+% \startsubsection[title={Flattening: \prm {mathflattenmode}}]
+%
+% \topicindex {math+flattening}
+%
+% The \TEX\ math engine collapses \type {ord} noads without sub- and superscripts
+% and a character as nucleus, which has the side effect that in \OPENTYPE\ mode
+% italic corrections are applied (given that they are enabled).
+%
+% \startbuffer[sample]
+% \switchtobodyfont[modern]
+% $V \mathbin{\mathbin{v}} V$\par
+% $V \mathord{\mathord{v}} V$\par
+% \stopbuffer
+%
+% \typebuffer[sample]
+%
+% This renders as:
+%
+% \blank \start \mathflattenmode\plusone \getbuffer[sample] \stop \blank
+%
+% When we set \prm {mathflattenmode} to 31 we get:
+%
+% \blank \start \mathflattenmode\numexpr1+2+4+8+16\relax \getbuffer[sample] \stop \blank
+%
+% When you see no difference, then the font probably has the proper character
+% dimensions and no italic correction is needed. For Latin Modern (at least till
+% 2018) there was a visual difference. In that respect this parameter is not always
+% needed unless of course you want efficient math lists anyway.
+%
+% You can influence flattening by adding the appropriate number to the value of the
+% mode parameter. The default value is~1.
+%
+% \starttabulate[|Tc|c|]
+% \DB mode \BC class \NC \NR
+% \TB
+% \NC  1   \NC ord   \NC \NR
+% \NC  2   \NC bin   \NC \NR
+% \NC  4   \NC rel   \NC \NR
+% \NC  8   \NC punct \NC \NR
+% \NC 16   \NC inner \NC \NR
+% \LL
+% \stoptabulate
+%
+% \stopsubsection
+
+\startsubsection[title={Less Tracing}]
+
+\topicindex {math+tracing}
+
+Because there are quite some math related parameters and values, it is possible
+to limit tracing. Only when \type {tracingassigns} and|/|or \type
+{tracingrestores} are set to~2 or more they will be traced.
+
+\stopsubsection
+
+\stopsection
+
+\startsection[title={Experiments}]
+
+There are a couple of experimental features. They will stay but details might
+change, for instance more control over spacing. We just show some examples and
+let your imagination work it out.
+
 \startsubsection[title={Forcing classes with \prm {Umathclass}}]
 
 You can change the class of a math character on the fly:
diff --git a/doc/context/sources/general/manuals/luametatex/luametatex-modifications.tex b/doc/context/sources/general/manuals/luametatex/luametatex-modifications.tex
index 083fa732a..054eec421 100644
--- a/doc/context/sources/general/manuals/luametatex/luametatex-modifications.tex
+++ b/doc/context/sources/general/manuals/luametatex/luametatex-modifications.tex
@@ -48,6 +48,14 @@ distribution, articles and presentations. It doesn't pay of to repeat that here,
 especially not in a time when users often search instead of read from cover to
 cover.
 
+Occasionally there are extensions to \PDFTEX\ and \LUATEX\ but these are unlikely
+to en dup in \LUAMETATEX. If needed one can add functionality using \LUA. Another
+reason is that because the way we handle files and generate output being
+compatible would only harm the engine. We have some fundamental extensions that
+overcome limitations anyway. One area where the are significate changes is in
+logging: at some point it no longer made sense to be compatible (with \LUATEX)
+because we carry around more information.
+
 \stopsubsection
 
 \startsubsection[title=Changes from \TEX\ 3.1415926...]
@@ -529,6 +537,17 @@ different extension to the original. You're warned.
 
 \stopsubsection
 
+\startsubsection[title=Changes in keyword scanning]
+
+\topicindex {keywords}
+
+Some primitives accept (optional) keywords and in \LUAMETATEX\ there are more
+keywords than in \LUATEX. Scanning can trigger error messages and lookahead side
+effects and in \LUAMETATEX\ these can be different. This is no big deal because
+errors are still errors.
+
+\stopsubsection
+
 \stopsection
 
 \stopchapter
diff --git a/doc/context/sources/general/manuals/luatex/luatex-nodes.tex b/doc/context/sources/general/manuals/luatex/luatex-nodes.tex
index 399713c41..e8a1701a3 100644
--- a/doc/context/sources/general/manuals/luatex/luatex-nodes.tex
+++ b/doc/context/sources/general/manuals/luatex/luatex-nodes.tex
@@ -890,6 +890,9 @@ The difference between \type {data} and \type {string} is that on assignment, th
 \type {data} field is converted to a token list, cf.\ use as \lpr {latelua}. The
 \type {string} version is treated as a literal string.
 
+When a function is used, it gets called with as first argument the node that triggers
+the call.
+
 \stopsection
 
 \startsection[title={\DVI\ backend whatsits}]
diff --git a/doc/context/sources/general/manuals/metafun/metafun-effects.tex b/doc/context/sources/general/manuals/metafun/metafun-effects.tex
index 0b7984e9e..787bd6f07 100644
--- a/doc/context/sources/general/manuals/metafun/metafun-effects.tex
+++ b/doc/context/sources/general/manuals/metafun/metafun-effects.tex
@@ -318,9 +318,9 @@ Of course this also works well for \CMYK\ colors.
 Gray scales work as well:
 
 \startbuffer
-\definecolor[ta][s=.9,t=.7,a=11]
-\definecolor[tb][s=.7,t=.7,a=11]
-\definecolor[tc][s=.5,t=.7,a=11]
+\definecolor[tgraya][s=.9,t=.7,a=11]
+\definecolor[tgrayb][s=.7,t=.7,a=11]
+\definecolor[tgrayc][s=.5,t=.7,a=11]
 \stopbuffer
 
 \typebuffer \getbuffer
@@ -339,9 +339,9 @@ difference in fonts.
 % \stopbuffer
 
 \startbuffer
-draw textext("\color[ta]{\tf Hello}") scaled 5 ;
-draw textext("\color[tb]{\bf Hello}") scaled 5 ;
-draw textext("\color[tc]{\sl Hello}") scaled 5 ;
+draw textext("\color[tgraya]{\tf Hello}") scaled 5 ;
+draw textext("\color[tgrayb]{\bf Hello}") scaled 5 ;
+draw textext("\color[tgrayc]{\sl Hello}") scaled 5 ;
 \stopbuffer
 
 \typebuffer
diff --git a/doc/context/sources/general/manuals/metafun/metafun.tex b/doc/context/sources/general/manuals/metafun/metafun.tex
index 8d3b513e0..a890f04c5 100644
--- a/doc/context/sources/general/manuals/metafun/metafun.tex
+++ b/doc/context/sources/general/manuals/metafun/metafun.tex
@@ -42,7 +42,7 @@
 %             I expect with the more efficient \LUA|-|\METAPOST\ interfacing). It also means
 %             that \LUAMETATEX|-|\LMTX\ is now comparable with \LUAJITTEX|-|\MKIV.
 
-% \enableexperiments[fonts.compact]
+\enableexperiments[fonts.compact]
 
 % \enablemode[optional]
 
diff --git a/doc/context/sources/general/manuals/ontarget/ontarget-anchoring.tex b/doc/context/sources/general/manuals/ontarget/ontarget-anchoring.tex
index 090c6ba0c..12852ba13 100644
--- a/doc/context/sources/general/manuals/ontarget/ontarget-anchoring.tex
+++ b/doc/context/sources/general/manuals/ontarget/ontarget-anchoring.tex
@@ -273,7 +273,6 @@ is also up to users to come up with demands.
 %              \hskip-2cm
 %              \blackrule[width=2cm,height=0cm,depth=1cm,color=darkyellow]}%
 %           %
-%         \smash{\box\scratchboxtwo}%
 %     \egroup
 % \stopbuffer
 %
diff --git a/doc/context/sources/general/manuals/ontarget/ontarget-math.tex b/doc/context/sources/general/manuals/ontarget/ontarget-math.tex
new file mode 100644
index 000000000..c7e5551d5
--- /dev/null
+++ b/doc/context/sources/general/manuals/ontarget/ontarget-math.tex
@@ -0,0 +1,1816 @@
+% language=us runpath=texruns:manuals/ontarget
+
+% \profilemacro\scaledfontdimen
+
+% \usebodyfont[modern]
+% \usebodyfont[cambria]
+% \usebodyfont[termes]
+% \usebodyfont[pagella]
+% \usebodyfont[bonum]
+
+\startcomponent ontarget-math
+
+\environment ontarget-style
+
+\startchapter[title={A different approach to math spacing}]
+
+\startsubject[title=Introduction]
+
+The \TEX\ engine is famous for its rendering of math and even after decades there
+is no real contender. And so there also is no real pressure to see if we can do
+better. However, when Mikael Sundqvist ran into a Swedish math rendering
+specification and we started discussing a possible support for that in \CONTEXT,
+it quickly became clear that the way \TEX\ does spacing is a bit less flexible
+than one wishes for. We already have much of what is needed in place but it also
+has to work well with how \TEX\ sees things:
+
+\startitemize[packed,n]
+\startitem
+    Math is made from a sequence of atoms: a quantity with a nucleus, superscript
+    subscript. \footnote {I suddenly realize why in the engine noads have a
+    nucleus field: they are atoms \unknown\ but what does that make super and
+    subscripts.} Atoms are spaced by \type {\thinmuskip}, \type {\medmuskip} and
+    \type {\thickmuskip} or nothing, and that is sort of hard coded.
+\stopitem
+\startitem
+    Atoms are organized by class and there are seven (or eight, depending on how
+    you look at it) of them visible: binary symbols, relations, etc. The
+    invisible ones, composites like fractions and fenced material (we call them
+    molecules) are at some point mapped onto the core set. Molecules like fences
+    have a different class left and right of the fenced material.
+\stopitem
+\startitem
+    In addition the engine itself has all kind of spacing related parameters and
+    these kick in automatically and sometimes have side effects. The same is
+    true for penalties.
+\stopitem
+\stopitemize
+
+The normal approach to spacing other than imposed by the engine is to use
+correction space, like \type {\,} and I think that quite some \TEX\ users think
+that this is how it is supposed to be. The standard way to enter math relates to
+scientific publishing and there the standards are often chiseled in stone so why
+should users tweak anyway. However, in \CONTEXT\ we tend to start from the users
+and not the publishers end so there we can decide to follow different routes.
+Users can always work around something they don't like but we focus on reliable
+input giving predictable output. Also, when reading on, it is good to realize
+that it is all about the user experience here: it should look nice (which then of
+course makes one become aware of issues elsewhere) and we don't care much about
+specific demands of publishers in the scientific field: the fact that they often
+re|-|key content doesn't go well with users paying attention themselves, let
+alone the fact that nowadays they can demand word processor formats.
+
+The three mentioned steps are fine for the average case but sometimes make no
+sense. It was definitely the best approach given time and resources but when
+\LUATEX\ went \OPENTYPE\ a lot of parameters were added and at that time we
+therefore added spacing by class pair. That not only decoupled the relation
+between the three (configurable) muskip parameters but also made it possible to
+use plenty of them. Now it must be said that for consistency having these three
+skips works great but given the tweaking expected from users consistency is
+not always what comes out.
+
+This situation is very well comparable to the proclaimed qualities of the
+typesetting of text by \TEX. Yes, it can do a great job, and often does, but users
+can mess up quite well. I remember that when we did tests with \HZ\ the outcomes
+were pretty unimpressive. When you give an audience a set of sample renderings,
+where each sample is slightly different and each user gets a randomized subset,
+the sudden lack of being able to compare (and agree) with another \TEX ie makes
+for interesting conclusions. They look for the opposites of what is claimed to be
+perfect. So, two lines with hyphens rate low, even if not doing it would look
+worse. The same for a few short words in the last line of a paragraph. Excessive
+spacing is also seen as bad. So, when asked why some paragraphs looked okay
+noticing (excessive and troublesome) expansion was not seen as a problem; instead
+it were hyphens that got the attraction.
+
+The same is probably true for math: the input with lots of correction spaces or
+commands where characters would do can be horrible but it's just the way it is
+supposed to be. The therefore expected output can only be perfect, right,
+independent of how one actually messed up spacing. But personally I think that it
+is often spacing messed up by users that make a \TEX\ document recognizable. It
+compares to word processor results that one can sometimes identify by multiple
+consecutive spaces in the typeset text instead of using a glue model like \TEX.
+Reaching perfection is not always trivial, but fortunately we can also find
+plenty of nice looking documents done with \TEX.
+
+The \TEX book has an excellent and intriguing chapter on the fine points of math
+and it definitely shows why Don Knuth wrote \TEX\ as a tool for his books. He
+pays a lot of attention to detail and that is also why it all works out so well.
+If you need to render from unseen sources (as happens in an \XML\ workflow)
+coming from several authors and have time nor money to check everything, you're
+off worse. And I'm not even talking of input where invisible \UNICODE\ spacing
+characters are injected. It is the \TEX\ book(s) that draw me to this program and
+believe it or not, in the first project I was involved in that demanded typeset
+(quantum mechanics) math the \IBM\ typewriter with changing bulbs ruled the
+scenery. In fact, our involvement was quickly cut off when we dared to show a
+chapter done in \TEX\ that looked better.
+
+Apart from an occasional tweak, in \CONTEXT\ we never really used this opened up
+math atom pair spacing mechanism available in \LUATEX\ extensively. So, when I
+was pondering how to proceed it stroke me that it would make sense to generalize
+this mechanism. It was already possible (via a mode parameter) to bypass the
+second step mentioned above, but we definitely needed more than the visible
+classes that the engine had. In \CONTEXT\ we already had more classes but those
+were meant for assigning characters and commands to specific math constructs
+(think of fences, fractions and radicals) so in the end they were not really
+classes. Considering this option was made easier by the fact that Mikael would do
+the testing and help configuring the defaults, which all will result in a new
+math user manual.
+
+There are extensions introduced in \LUATEX\ and later \LUAMETATEX\ that are not
+discussed here. In this expose we concentrate on the features that were explored,
+extended and introduced while we worked on updating math support in \LMTX.
+
+\stopsubject
+
+\startsubject[title=An example]
+
+Before we go into details, let's give an example of unnoticed spacing effects. We
+use three simple formulas all using fractions:
+
+\startbuffer[one]
+\ruledhbox{$\frac{x^2}{a+1}$}
+\stopbuffer
+
+\startbuffer[two]
+\ruledhbox{$x + \frac{x^2}{a+1} = 10$}
+\stopbuffer
+
+\startbuffer[three]
+\ruledhbox{$\frac{1}{2}\frac{1}{2}x$}
+\stopbuffer
+
+\typebuffer[one]
+
+and:
+
+\typebuffer[two]
+
+as well as:
+
+\typebuffer[three]
+
+\startbuffer[all]
+\dontleavehmode
+\scale[scale=4000]{\getbuffer[one]}
+\scale[scale=4000]{\getbuffer[two]}
+\scale[scale=4000]{\getbuffer[three]}
+\stopbuffer
+
+\startlinecorrection
+\nulldelimiterspace=1.2pt\getbuffer[all]
+\stoplinecorrection
+
+If you look closely you see that the fraction has a little space at the left and
+right. Where does that come from? Because we normally don't put a tight frame
+around a fraction, we are not really aware of it. The spacing between what are
+called ordinary, operator, binary, relation and other classes of atoms is
+explained in the \TEX book (or \quotation {\TEX\ by Topic} if you want a summary)
+and basically we have a class by class matrix that is built into \TEX. The
+engine looks at successive items and spacing depends on their (perceived) class.
+Because the number of classes is limited, and because the spacing pairs are hard
+coded, the engine cheats a little. Depending on what came before or comes next
+the class of an atom is adapted to suit the spacing matrix. One can say that a
+\quotation {reading mathematician} is built in. And most of the decisions are
+okay. If needed one can always wrap something in e.g.\ \type {\mathrel} but of
+course that also can interfere with grouping. All this is true for \TEX, \PDFTEX,
+\XETEX\ and \LUATEX, but a bit different in \LUAMETATEX\ as we will see.
+
+The little spacing on both edges of the fraction is a side effect of the way they
+are build internally: fractions are actually a generalized form of \quotation
+{stuff put on top of other stuff} and they can have left and|/|or right
+delimiters: this is driven by primitives that have names like \type {\atop} and
+\type {\atopwithdelims}. The way the components are placed is (especially in the
+case of \OPENTYPE) driven by lots of parameters and I will leave that out of the
+discussion.
+
+When there are no delimiters, a so called \type {\nulldelimiterspace} will be
+injected. That parameter is set to 1.2 points and I have to admit that in
+\CONTEXT\ I never considered letting that one adapt to the body font size, which
+means that, as we default to a 12 point body font, the value there should have
+been 1.44 points: mea culpa. When we set this parameter to zero point, we get
+this:
+
+\startlinecorrection
+\nulldelimiterspace=0pt\getbuffer[all]
+\stoplinecorrection
+
+As intermezzo and moment of contemplation I show some examples of fractions mixed
+into text. When we have the delimiter space set we get this:
+
+\start \nulldelimiterspace=1.2pt \dorecurse{100}{test $\frac{1}{#1}$ } \stop
+
+While with zero it looks like this, quite a different outcome:
+
+\start \nulldelimiterspace=0pt   \dorecurse{100}{test $\frac{1}{#1}$ } \stop
+
+A little tracing shows it more clearly:
+
+\start \showboxes \nulldelimiterspace=1.2pt \dorecurse{100}{test $\frac{1}{#1}$ } \stop
+
+You can zoom in and see where it interferes with margin alignment.
+
+\start \showboxes \nulldelimiterspace=0pt   \dorecurse{100}{test $\frac{1}{#1}$ } \stop
+
+So, if you ever meet a user who claims perfection and superiority of typesetting,
+check out her|/|his work which might have inline fractions done the spacy way. It
+might make other visually typesetting claims less trustworthy. And yes, one can
+wonder if margin kerning could help here but as this content is wrapped in boxes it
+is unlikely to work out well (and not worth the effort).
+
+In order to get a better picture of the spacing, two more renderings are shown.
+This time we show the bounding boxes of the characters too (you might need to zoom
+in to see it):
+
+\startlinecorrection
+\showglyphs\nulldelimiterspace=1.2pt\getbuffer[all]
+\stoplinecorrection
+
+Again we also show the zero case
+
+\startlinecorrection
+\showglyphs\nulldelimiterspace=0pt\getbuffer[all]
+\stoplinecorrection
+
+This makes clear why there actually is this extra space around a fraction:
+regular operators have side bearings and thereby have some added space. And when
+we put a fraction in front of a symbol we need that little extra space. Of course
+a proper class pair spacing value could do the job but there is no fraction
+class. The engine cheats by changing the class depending on what follows or came
+before and this is why on the average it looks okay. However, these examples
+demonstrate that there are some assumptions with regard to for instance fonts
+and this is one of the reasons why the more or less official expected \OPENTYPE\
+behavior as dictated by the Cambria font doesn't always work out well for fonts
+that evolved from the ones used in the \TEX\ community. Also imagine how this
+interferes with the fact that traditional \TEX\ fonts and the machinery do magic
+with cheating about width combined with italic correction (all plausible and
+quite clever but somewhat tricky with respect to \OPENTYPE).
+
+Because here we discuss the way \LUAMETATEX\ and \CONTEXT\ deal with this, the
+next examples show a probably unexpected outcome. Again first the non|-|zero
+case:
+
+\startlinecorrection
+\showglyphs\showmakeup[mathglue]\nulldelimiterspace=1.2pt\getbuffer[all]
+\stoplinecorrection
+
+And here the zero case:
+
+\startlinecorrection
+\showglyphs\showmakeup[mathglue]\nulldelimiterspace=0pt\getbuffer[all]
+\stoplinecorrection
+
+I will not go into details about the way fractions are supported in the engine
+because some extensions are already around for quite a while. The main
+observation here is that in \LUAMETATEX\ we have alternative primitives that
+assume forward scanning, as if the numerator and denominator are arguments. The
+engine also supports skewed (vulgar) fractions natively where numerator and
+denominator are raised and lowered relative to the (often) slash. Many aspects
+of the rendering can be tuned in the so called font goodie files, which is also
+the place where we define the additional font parameters.
+
+\stopsubject
+
+\startsubject[title=Atom spacing]
+
+If you are familiar with traditional \TEX\ you know that there is some build in
+\type {ordbin} spacing. But there is no such pair for a fraction and a relation,
+simply because there is no fraction class. However, in \LUAMETATEX\ there is one,
+and we'd better set it up if we zero the margins of a fraction.
+
+It is worth noticing that fractions are sort of special anyway. The official
+syntax is \type {n \over m} and numerator and denominator can be sub formulas.
+This is the one case where the parser sort of has to look back, which is tricky
+because the machinery is a forward looking one. Therefore, in order to get the
+expected styling (or avoid unexpected side effects) one will normally wrap all in
+braces as in: \type {{ {n} \over {m} }} which of course kind defeats the simple
+syntax which probably is supported for \type {1\over2} kind of usage, so a next
+challenge is to make \type {1/2} come out right. All this means that in practice
+we have wrappers like \type {\frac} which accidentally in \LUAMETATEX\ can be
+defined using forward looking primitives with plenty extra properties driven by
+keywords. It also means that fractions as expected by the engine due to wrapping
+actually can be a different kind of atom, which can have puzzling side effects
+with respect to spacing (because the remapping happens unseen).
+
+Interesting is that adapting \LUAMETATEX\ to a more extensive model was quite
+doable, also because the code base had already be made more configurable. Of
+course it involved quite a bit of tedious editing and throwing out already nice
+and clean code that had taken some effort, but that's the way it is. Of course
+more classes also means that some storage properties had to be adapted within the
+available space but by sacrificing families that was possible. With 64 potential
+classes we now are back to 64 families compared to 7 classes and 256 families in
+\LUATEX\ and 7 classes and 16 families in traditional \TEX.
+
+Also interesting is that the new implementation is actually somewhat simpler and
+therefore the binary is a tad smaller too. But does all that mean that there were
+no pitfalls? Sure there were! It is worth noticing that doing all this reminded
+me of the early days of \LUATEX\ development, where Taco and I exchanged binaries
+and \TEX\ code in a more or less constant way using Skype. For \LUAMETATEX\ we
+used good old mail for files and Mojca's build farm for binaries and Mikael and I
+spent many month exchanging information and testing out alternatives on a daily
+basis: it is in my opinion the only way to do this and it's fun too. It has been
+a lot of work but once we got going there was nothing that could stop us. A side
+effect was that there were no updates during this period, which was something
+users noticed.
+
+In the spacing matrix there is \type {inner} and internally there's also some
+care to be taken of \type {vcenter}. The \type {inner} class is actually shared
+with the \type {variable} class which is not so much a real class but more a
+signal to the engine that when an alphabetic or numeric character is included that
+it has to come from a specific family: upright family zero or math italic family
+one in traditional speak. But, what if we don't have that setup? Well, then one
+has to make sure that this special class number is not associated (which is no
+big deal). It does mean that when we extend the repertoire of classes we
+cannot use slot seven. Always keep in mind that classes (and thereby signals) get
+assigned to characters (some defaults by the engine, others by the macro
+package). It is why in \CONTEXT\ we use abstract class numbers, just in case the
+engine gets adapted.
+
+We also cannot use slot eight because that one is a signal too: for a possible
+active math character, a feature somewhat complicated by the fact that it should
+not interfere with passing around such active characters in arguments. In math
+mode where we have lots of macros passing around content, this special class works
+around these side effects. We don't need this feature in \CONTEXT\ because
+contrary to other macro packages we don't handle primes, pseudo superscripts
+potentially followed by other super and subscripts by making the \type {'} an
+active character and thereby a macro in math mode. This trickery again closely
+relates to preferable input, font properties, and limitations of memory and such
+at the time \TEX\ showed up (much has to fit into 8, 16 or 32 bits, so there is
+not much room for e.g.\ more than 8 classes). Since we started with \MKIV\ the way
+math is dealt with is a bit different than normally done in \TEX\ anyway.
+
+\stopsubject
+
+\startsubject[title=Atom rules]
+
+We can now control the spacing between every atom but unfortunately that is not
+good enough. Therefore, we arrive at yet another feature built into the engine:
+turning classes into other classes depending on neighbors. And this is precisely
+why we have certain classes. Let's quote \quotation {\TEX\ by Topic}: {\em The
+cases \type {*} (in the atom spacing matrix) cannot occur, because a \type {bin}
+object is converted to \type {ord} if it is the first in the list, preceded by
+\type {bin}, \type {op}, \type {open}, \type {punct}, \type {rel}, or followed by
+\type{close}, \type {punct}, or \type {rel}; also, a \type{rel} is converted to
+\type{ord} when it is followed by \type {close} or \type {punct}.}
+
+We can of course keep these hard coded heuristics but can as well make that bit
+of code configurable, which we did. Below is demonstrated how one can set up the
+defaults at the \TEX\ end. We use symbolic names for the classes.
+
+\starttyping
+\setmathatomrule  \mathbegincode         \mathbinarycode       % old
+  \allmathstyles    \mathordinarycode      \mathordinarycode   % new
+
+\setmathatomrule  \mathbinarycode        \mathbinarycode
+  \allmathstyles    \mathbinarycode        \mathordinarycode
+\setmathatomrule  \mathoperatorcode      \mathbinarycode
+  \allmathstyles    \mathoperatorcode       \mathordinarycode
+\setmathatomrule  \mathopencode          \mathbinarycode
+  \allmathstyles    \mathopencode          \mathordinarycode
+\setmathatomrule  \mathpunctuationcode   \mathbinarycode
+  \allmathstyles    \mathpunctuationcode   \mathordinarycode
+\setmathatomrule  \mathrelationcode      \mathbinarycode
+  \allmathstyles    \mathrelationcode      \mathordinarycode
+
+\setmathatomrule  \mathbinarycode        \mathclosecode
+  \allmathstyles    \mathordinarycode      \mathclosecode
+\setmathatomrule  \mathbinarycode        \mathpunctuationcode
+  \allmathstyles    \mathordinarycode      \mathpunctuationcode
+\setmathatomrule  \mathbinarycode        \mathrelationcode
+  \allmathstyles    \mathordinarycode      \mathrelationcode
+
+\setmathatomrule  \mathrelationcode      \mathclosecode
+  \allmathstyles    \mathordinarycode      \mathclosecode
+\setmathatomrule  \mathrelationcode      \mathpunctuationcode
+  \allmathstyles    \mathordinarycode      \mathpunctuationcode
+\stoptyping
+
+Watch the special class with \type {\mathbegincode}. This is actually class 62 so
+you don't need much fantasy to imagine that class 63 is \type {\mathendcode}, but
+that one is not yet used. In a similar fashion we can initialize the spacing
+itself: \footnote {Constant, engine specific, numbers like these are available in
+tables at the \LUA\ end so we can change them and users can check that.}
+
+\starttyping
+\setmathspacing \mathordcode   \mathopcode     \allmathstyles  \thinmuskip
+\setmathspacing \mathordcode   \mathbincode    \allsplitstyles \medmuskip
+\setmathspacing \mathordcode   \mathrelcode    \allsplitstyles \thickmuskip
+\setmathspacing \mathordcode   \mathinnercode  \allsplitstyles \thinmuskip
+
+\setmathspacing \mathopcode    \mathordcode    \allmathstyles  \thinmuskip
+\setmathspacing \mathopcode    \mathopcode     \allmathstyles  \thinmuskip
+\setmathspacing \mathopcode    \mathrelcode    \allsplitstyles \thickmuskip
+\setmathspacing \mathopcode    \mathinnercode  \allsplitstyles \thinmuskip
+
+\setmathspacing \mathbincode   \mathordcode    \allsplitstyles \medmuskip
+\setmathspacing \mathbincode   \mathopcode     \allsplitstyles \medmuskip
+\setmathspacing \mathbincode   \mathopencode   \allsplitstyles \medmuskip
+\setmathspacing \mathbincode   \mathinnercode  \allsplitstyles \medmuskip
+
+\setmathspacing \mathrelcode   \mathordcode    \allsplitstyles \thickmuskip
+\setmathspacing \mathrelcode   \mathopcode     \allsplitstyles \thickmuskip
+\setmathspacing \mathrelcode   \mathopencode   \allsplitstyles \thickmuskip
+\setmathspacing \mathrelcode   \mathinnercode  \allsplitstyles \thickmuskip
+
+\setmathspacing \mathclosecode \mathopcode     \allmathstyles  \thinmuskip
+\setmathspacing \mathclosecode \mathbincode    \allsplitstyles \medmuskip
+\setmathspacing \mathclosecode \mathrelcode    \allsplitstyles \thickmuskip
+\setmathspacing \mathclosecode \mathinnercode  \allsplitstyles \thinmuskip
+
+\setmathspacing \mathpunctcode \mathordcode    \allsplitstyles \thinmuskip
+\setmathspacing \mathpunctcode \mathopcode     \allsplitstyles \thinmuskip
+\setmathspacing \mathpunctcode \mathrelcode    \allsplitstyles \thinmuskip
+\setmathspacing \mathpunctcode \mathopencode   \allsplitstyles \thinmuskip
+\setmathspacing \mathpunctcode \mathclosecode  \allsplitstyles \thinmuskip
+\setmathspacing \mathpunctcode \mathpunctcode  \allsplitstyles \thinmuskip
+\setmathspacing \mathpunctcode \mathinnercode  \allsplitstyles \thinmuskip
+
+\setmathspacing \mathinnercode \mathordcode    \allsplitstyles \thinmuskip
+\setmathspacing \mathinnercode \mathopcode     \allmathstyles  \thinmuskip
+\setmathspacing \mathinnercode \mathbincode    \allsplitstyles \medmuskip
+\setmathspacing \mathinnercode \mathrelcode    \allsplitstyles \thickmuskip
+\setmathspacing \mathinnercode \mathopencode   \allsplitstyles \thinmuskip
+\setmathspacing \mathinnercode \mathpunctcode  \allsplitstyles \thinmuskip
+\setmathspacing \mathinnercode \mathinnercode  \allsplitstyles \thinmuskip
+\stoptyping
+
+And because we have a few more atom classes this also needs to happen:
+
+\starttyping[style=\tt]
+\letmathspacing  \mathactivecode   \mathordinarycode
+\letmathspacing  \mathvariablecode \mathordinarycode
+\letmathspacing  \mathovercode     \mathordinarycode
+\letmathspacing  \mathundercode    \mathordinarycode
+\letmathspacing  \mathfractioncode \mathordinarycode
+\letmathspacing  \mathradicalcode  \mathordinarycode
+\letmathspacing  \mathmiddlecode   \mathopencode
+\letmathspacing  \mathaccentcode   \mathordinarycode
+
+\letmathatomrule \mathactivecode   \mathordinarycode
+\letmathatomrule \mathvariablecode \mathordinarycode
+\letmathatomrule \mathovercode     \mathordinarycode
+\letmathatomrule \mathundercode    \mathordinarycode
+\letmathatomrule \mathfractioncode \mathordinarycode
+\letmathatomrule \mathradicalcode  \mathordinarycode
+\letmathatomrule \mathmiddlecode   \mathopencode
+\letmathatomrule \mathaccentcode   \mathordinarycode
+\stoptyping
+
+With \type {\resetmathspacing} we get an all|-|zero state but that might become
+more refined in the future. What is not clear from the above is that there is
+also an inheritance mechanism. The three special muskip registers are actually
+shortcuts so that changing the register value is reflected in the spacing. When a
+regular muskip value is (verbose or as register) that value is sort of frozen.
+However, the \type {\inherited} prefix will turn references to registers and
+constants into a delayed value: as with the predefined we now have a more dynamic
+behavior which means that we can for instance use reserved muskip registers as we
+can use the predefined. A bonus is that one can also use regular glue or
+dimensions, just in case one wants the same spacing in all styles (a muskip
+adapts to the size).
+
+When you look at all the above you might wonder how users are supposed to deal
+with math spacing. The answer is that often they can just assume that \TEX\ does
+the right thing. If something somehow doesn't feel right, looking at solutions by
+others will probably lead a new user to just copy a trick, like injecting a \type
+{\thinmuskip}. But it can be that atoms depend on the already applied (or not)
+spacing, which in turn depends on values in the atom spacing matrix that probably
+only a few users have seen. So, in the end it all boils down to trust in the
+engine and one's eyesight combined with hopefully some consistency in adding
+space directives and often with \TEX\ it is consistency that makes documents look
+right. In \CONTEXT\ we have many more classes even if only a few characters fit in,
+like differential, exponential and imaginary.
+
+\stopsubject
+
+\startsubject[title=Fractions again]
+
+We now return to the fraction molecule. With the mechanisms at our disposal we
+can change the fixed margins to more adaptive ones:
+
+\starttyping
+\inherited\setmathspacing \mathbinarycode   \mathfractioncode
+    \allmathstyles \thickermuskip
+\inherited\setmathspacing \mathfractioncode \mathbinarycode
+    \allmathstyles \thickermuskip
+\nulldelimiterspace\zeropoint
+$x + \frac{1}{x+2} + x$
+\stoptyping
+
+Here \typ {\thickermuskip} is defined as \type {7mu plus 5mu} where the stretch
+is the same as a \typ {\thickmuskip} and the width \type {2mu} more. We start out
+with three variants, where the last two have \typ {\nulldelimiterspace} set to
+\type {0pt} and the first one uses the \type {1.2pt}.
+
+\definecolor[tred]  [r=1,a=1,t=.5]
+\definecolor[tgreen][g=1,a=1,t=.5]
+\definecolor[tblue] [b=1,a=1,t=.5]
+
+\startlinecorrection
+\scale[scale=4000]\bgroup\vbox\bgroup \forgetall
+    \bgroup \tgreen \nulldelimiterspace=1.2pt $x + \frac{1}{x+2} + x$\egroup\par
+    \bgroup \tred   \nulldelimiterspace=0.0pt $x + \frac{1}{x+2} + x$\egroup\par
+    \bgroup \tblue  \nulldelimiterspace=0.0pt $x + \frac{1}{x+2} + x$\egroup\par
+\egroup\egroup
+\stoplinecorrection
+
+When we now apply the new settings to the last one, and overlay them we get the
+following output: the first and last case are rather similar which is why this
+effort was started in the first place.
+
+\startlinecorrection
+\scale[scale=4000]\bgroup
+    \startoverlay
+        \bgroup
+            \inherited\setmathspacing \mathbinarycode   \mathfractioncode \allmathstyles \thickmuskip
+            \inherited\setmathspacing \mathfractioncode \mathbinarycode   \allmathstyles \thickmuskip
+            \tgreen \nulldelimiterspace=1.2pt $x + \frac{1}{x+2} + x$
+        \egroup
+        \bgroup
+            \inherited\setmathspacing \mathbinarycode   \mathfractioncode \allmathstyles \thickmuskip
+            \inherited\setmathspacing \mathfractioncode \mathbinarycode   \allmathstyles \thickmuskip
+            \tred \nulldelimiterspace=0.0pt $x + \frac{1}{x+2} + x$
+        \egroup
+        \bgroup
+            \inherited\setmathspacing \mathbinarycode   \mathfractioncode \allmathstyles \thickermuskip
+            \inherited\setmathspacing \mathfractioncode \mathbinarycode   \allmathstyles \thickermuskip
+            \tblue \nulldelimiterspace=0.0pt $x + \frac{1}{x+2} + x$
+        \egroup
+    \stopoverlay
+\egroup
+\stoplinecorrection
+
+Of course this kind of changes are not upward compatible but as they are tiny
+they are not that likely to change the number of lines in a paragraph. In display
+mode changes in horizontal dimensions also hav elittle effect.
+
+\startsubject[title=Penalties]
+
+An inline formula can be broken across lines, and for sure there are places where
+you don't want to break or prefer to break. In \TEX\ line breaks can be
+influenced by using penalties. At the outer level of an inline math formula, we
+can have a specific penalty before and after a binary and|/|or relation. The
+defaults are such that there are no penalties set, but most macro packages set
+the so called \type {\relpenalty} and \type {\binoppenalty} (the \type {op} in
+this name does not relate to the operator class) so a value between zero and
+1000. In \LUATEX\ we also have \type{\pre} variants of these, so we have four
+penalties that can be set, but that is not enough in our new approach.
+
+These penalties are class bound and don't relate to styles, like atom spacing
+does. That means that while atom spacing involves $64 \times 64 \times 8$
+potential values, an amount that we can manage by using the discussed
+inheritance. The inheritance takes less values because which store 4 style values
+per class in one number. For penalties we only need to keep $64 \times 2$ in
+mind, plus a range of inheritance numbers. Therefore it was decided to also
+generalize penalties so that each class can have them. The magic commands are
+shown with some useless examples:
+
+\starttyping
+\letmathparent \mathdigitcode
+    \mathbincode   % pre penalty
+    \mathbincode   % post penalty
+    \mathdigitcode % options
+    \mathdigitcode % reserved
+\stoptyping
+
+By default the penalties are on their own, like:
+
+\starttyping
+\letmathparent \mathdigitcode
+  \mathdigitcode % pre penalty
+  \mathdigitcode % post penalty
+  \mathdigitcode % options
+  \mathdigitcode % reserved
+\stoptyping
+
+The options and reserved parent mapping are not (yet) discussed here. Unless
+values are assigned they are ignored.
+
+\starttyping
+\setmathprepenalty  \mathordcode 100
+\setmathpostpenalty \mathordcode 600
+\setmathprepenalty  \mathbincode 200
+\setmathpostpenalty \mathbincode 700
+\setmathprepenalty  \mathrelcode 300
+\setmathpostpenalty \mathrelcode 800
+\stoptyping
+
+As with spacing, when there is no known value, the parent will be consulted. An unset
+penalty has a value of 10000.
+
+After discussing the implications of inline math crossing lines, Mikael and I
+decided that there can be two solutions. Both can of course be implemented in
+\LUA, but on the other hand, they make good extensions, also because it sort of
+standardized it. The first advanced control feature tweaks penalties:
+
+\starttyping
+\mathforwardpenalties  2  200 100
+\mathbackwardpenalties 2  100  50
+\stoptyping
+
+This will add 200 and 100 to the first two math related penalties, and 100 and 50
+to the last two (watch out: the 100 will be assigned to the last found one, the
+50 to the one before it). As with all things penalty and line break related, you
+need to have some awareness of how non|-|linear the badness calculation is as
+well of the fact that the tolerance and stretch related parameters play a role
+here.
+
+The second tweak is setting \type {\maththreshold} to some value. When set to for
+instance \type {40pt}, formulas that take less space than this will be wrapped in
+a \type {\hbox} and thereby will never break across a page. \footnote {A future
+version might inject severe penalties instead, time will learn.} Actually that
+second tweak has a variant so we have three tweaks! Say that we have this sample
+formula wrapped in some bogus text and repeat that snippet a lot of times:
+
+\startbuffer[demo]
+x xx xxx xxxx $1 + x$ x xx xxx xxxx
+\stopbuffer
+
+\typebuffer[demo]
+
+Now look at the example on the next page. You will notice that the red and blue
+text have different line breaks. This is because we have given the threshold some
+stretch and shrink. The red text has a zero threshold so it doesn't do any magic
+at all, while the second has this setup:
+
+\startbuffer
+\setupmathematics[threshold=medium]
+\stopbuffer
+
+That setting set the threshold to \typ {4em plus 0.75em minus 0.50em} and when
+the formula size exceeds the four quads the line break code will use the real
+formula width but with the given stretch and shrink. Eventually the calculated
+size will be used to repackage the formula. In the future we will also provide a
+way to define slack more relative to the size and|/|or number of atoms.
+
+\startpostponing
+\startlinecorrection \small
+\startoverlay
+    {\setupmathematics[threshold=none]%
+     \vbox\bgroup
+        \darkred
+        \dorecurse {40} {\getbuffer[demo]}
+     \egroup}
+    {\setupmathematics[threshold=medium]%
+     \vbox\bgroup
+        \darkblue
+        \dorecurse {40} {\getbuffer[demo]}
+     \egroup}
+\stopoverlay
+\stoplinecorrection
+\stoppostponing
+
+Another way to influence line breaks is to use the two inline math related
+penalties that have been added at Mikael's suggestion:
+
+\startbuffer \setupalign[verytolerant]
+{\dorecurse{25}{test $\darkred   #1^{#1} + x_{#1}^{#1}$ test }\blank}
+{\preinlinepenalty  500 \postinlinepenalty -500
+ \dorecurse{25}{test $\darkgreen #1^{#1} + x_{#1}^{#1}$ test }\blank}
+{\postinlinepenalty 500 \preinlinepenalty  -500
+ \dorecurse{25}{test $\darkblue  #1^{#1} + x_{#1}^{#1}$ test }\blank}
+\stopbuffer
+
+\typebuffer
+
+To get an example that shows the effect takes a bit of trial and error because
+\TEX\ does a very good job in line breaking. This is why we've set the tolerance
+and also use negative penalties.
+
+In addition to the \type {\mathsurround} (kern) and \type {\mathsurroundskip}
+(glue) parameters this is a property of the nodes that mark the beginning and end
+of an inline math formula.
+
+\blank \getbuffer \blank
+
+\stopsubject
+
+\startsubject[title=Flattening]
+
+The traditional engine has some code for flattening math constructs that in the
+end are just one character. So in the end, \type {\tilde {u}} and \type {\tilde
+{uu}} become different objects even if both are in fact accents. In fact, when an
+accent is constructed there is a special code path for single characters so that
+script placement adapts to the shape of that character.
+
+However because of interaction with primes, which themselves are sort of
+superscripts and due to the somewhat weird way fonts provide them when it comes
+to positioning and sizes, in \CONTEXT\ we already are fooling around a bit with
+these characters. For understandable reasons of memory usage, complexity and
+eightbitness primes are not a native \TEX\ thing but more something that is
+handled at the macro level (although not in \MKIV\ and \LMTX).
+
+In the end it was script placements on (widely) accented math characters that
+made us introduced a dedicated \type {\Umathprime} primitive that adds a prime to
+a math atom. It permits an uninterupted treatment of scripts while in the final
+assembly of the molecule the prime, superscript, subscript and maybe even
+prescripts that prime gets squeezed in. Because the concept of primes is missing
+in \OPENTYPE\ math an additional font parameter \type {PrimeTopRaisePercent} has
+been introduced as well as an \type {\Umathprimeraise} primitive. In retrospect I
+should have done that earlier but one tends to stick to the original as much as
+possible. However, at some point Mikael and I reached a state where we decided
+that proper (clean) engine extensions make way more sense than struggling with
+border cases and explaining users why things are so complicated.
+
+The input \type {$ X \Uprimescript{'} ^2 _3 $} gives this:
+
+\startlinecorrection
+\startcombination[nx=4,distance=3em,inbetween={\blank[3*medium]}]
+    {\switchtobodyfont [modern]\removeunwantedspaces\scale[s=5]{\strut$\showboxes\showglyphs X\Uprimescript{'}^2_3$}} {Latin Modern}
+    {\switchtobodyfont[cambria]\removeunwantedspaces\scale[s=5]{\strut$\showboxes\showglyphs X\Uprimescript{'}^2_3$}} {Cambria}
+    {\switchtobodyfont[pagella]\removeunwantedspaces\scale[s=5]{\strut$\showboxes\showglyphs X\Uprimescript{'}^2_3$}} {Pagella}
+    {\switchtobodyfont [dejavu]\removeunwantedspaces\scale[s=5]{\strut$\showboxes\showglyphs X\Uprimescript{'}^2_3$}} {Dejavu}
+\stopcombination
+\stoplinecorrection
+
+With \type {\tracingmath = 1} this nicely traces as:
+
+\starttyping
+> \inlinemath=
+\mathord
+.\nucleus
+..\mathchar (fam="0,char="58)
+.\superscript
+..\mathchar (fam="0,char="32)
+.\subscript
+..\mathchar (fam="0,char="32)
+.\primescript
+..\mathchar (fam="0,char="27)
+\stoptyping
+
+Of course this feature scan also be used for other prime like ornaments and who
+knows how it will evolve over time.
+
+You can influence the positioning with \type {\Umathprimesupshift} which adds
+some kern between a prime and superscript. The \type {\Umathextraprimeshift}
+moves a prime up. The \type {\Umathprimeraise} is a font parameter that defaults
+to 25 which means a raise of 25\percent of the height. These are all (still)
+experimental parameters.
+
+\stopsubject
+
+\startsubject[title=Fences]
+
+Fences can be good for headaches. Because the math that I (or actually my
+colleague) deal with is mostly school math encoded in presentation \MATHML\ (sort
+or predictable) or some form of sequential \ASCII\ based input (often rather
+messy and therefore unpredictable due to ambiguity) fences are a pain. A \TEX ie
+can make sure that left and right fenced are matched. A \TEX ie also knows when
+something is an inline parenthesis or when a more high level structure is needed,
+for instance when parentheses have to scale with what they wrap. In that case the
+\type {\left} and \type {\right} mechanism is used. In arbitrary input missing
+one of those is fatal. Therefore, handling of fences in \CONTEXT\ is one of the
+more complex sub mechanisms: we not only need to scale when needed, but also
+catch asymmetrical usage.
+
+A side effect of the encapsulating fencing construct is that it wraps the content
+in a so called inner (as in \type {\mathinner}) which means that we get a box,
+and it is a well known property of boxes that they don't break across lines. With
+respect to fences, a way out is to not really fence content, but do something
+like this:
+
+\starttyping
+\left(\strut\right. x + 1 \left.\strut\right)
+\stoptyping
+
+and hope for the best. Both pairs are coupled in the sense that their sizes will
+match and the strut is what determines the size. So, as long as there is a proper
+match of struts all is well, but it is definitely a decent hack. The drawback is
+in the size of the strut: if a formula needs a higher one, larger struts have to
+be used. This is why in plain \TEX\ we have these commands:
+
+\starttyping[style=\small\tt]
+\def\bigl {\mathopen \big } \def\bigm {\mathrel\big } \def\bigr {\mathclose\big }
+\def\Bigl {\mathopen \Big } \def\Bigm {\mathrel\Big } \def\Bigr {\mathclose\Big }
+\def\biggl{\mathopen \bigg} \def\biggm{\mathrel\bigg} \def\biggr{\mathclose\bigg}
+\def\Biggl{\mathopen \Bigg} \def\Biggm{\mathrel\Bigg} \def\Biggr{\mathclose\Bigg}
+
+\def\big #1{{\hbox{$\left#1\vbox to  8.5pt{}\right.\nomathspacing$}}}
+\def\Big #1{{\hbox{$\left#1\vbox to 11.5pt{}\right.\nomathspacing$}}}
+\def\bigg#1{{\hbox{$\left#1\vbox to 14.5pt{}\right.\nomathspacing$}}}
+\def\Bigg#1{{\hbox{$\left#1\vbox to 17.5pt{}\right.\nomathspacing$}}}
+
+\def\nomathspacing{\nulldelimiterspace0pt\mathsurround0pt} % renamed
+\stoptyping
+
+The middle is kind of interesting because it has relation properties, while the
+\type {\middle} introduced in \ETEX\ got open properties, but we leave that
+aside.
+
+In \CONTEXT\ we have plenty of alternatives, including these commands, but they
+are defined differently. For instance they adapt to the font size. The hard coded
+point sizes in the plain \TEX\ code relates to the font and steps available in
+there (either by next larger or by extensible). The values thereby need to be
+adapted to the chosen body font as well as the body font size. In \MKIV\ and even
+better in \LMTX\ we can actually consult the font and get more specific sizes.
+
+But, this section is not about how to get these fixed sizes. Actually, the need
+to choose explicitly is not what we want, especially because \TEX\ can size
+delimiters so well. So, take this code snippet:
+
+\startbuffer
+$ x = \left( \dorecurse{40}{\frac{x}{x+#1} +} x \right) $
+\stopbuffer
+
+\typebuffer
+
+% \dostepwiserecurse{0}{25}{1}{
+% \begingroup \showmakeup[mathglue] \showglyphs
+% \advance\hsize-#1pt\relax \inleftmargin{#1pt}%
+% $ x = \left( \dorecurse{20}{\frac{x}{x+##1} +} x \right) $
+% \blank \endgroup
+% }
+When we typeset this inline, as in \inlinebuffer, we get nicely scaled fences but
+in a way that permits line breaks. The reason is that the engine has been
+extended with a \type {fenced} class so that we can recognize later on,
+when \TEX\ comes to injecting spaces and penalties, that we need to unpack the
+construct. It is another beneficial side effect of the generalization.
+
+The Plain \TEX\ code can be used to illustrate some of what we discussed before
+about fractions. In the next code we use excessive delimiter spacing:
+
+\starttyping
+\def\Bigg#1{%  watch the wrapping in a box
+  {%
+    \hbox {%
+        $\normalleft#1\vbox to 17.5pt{}\normalright.\nomathspacing$%
+    }%
+  }%
+}
+
+\nulldelimiterspace0pt
+\def\nomathspacing{\nulldelimiterspace0pt\mathsurround0pt}
+
+$\Bigg( 1 + x\Bigg) \quad \Bigg( \frac{1}{x}\Bigg)$\par
+
+\nulldelimiterspace10pt
+\def\nomathspacing{\nulldelimiterspace0pt\mathsurround0pt}
+
+$\Bigg( 1 + x\Bigg) \quad \Bigg( \frac{1}{x}\Bigg)$\par
+
+\nulldelimiterspace10pt
+\def\nomathspacing{\mathsurround0pt}
+
+$\Bigg( 1 + x\Bigg) \quad \Bigg( \frac{1}{x}\Bigg)$\par
+\stoptyping
+
+This renders as follows. We explicitly set \type {\nulldelimiterspace} to values
+because in \CONTEXT\ it is now zero by default.
+
+\startlinecorrection
+    \pushoverloadmode
+    \def\Bigg#1{{\hbox{$\normalleft#1\vbox to 17.5pt{}\normalright.\nomathspacing$}}}
+    \popoverloadmode
+    \startcombination[nx=3,ny=1,distance=3em]
+        {\showboxes
+         \nulldelimiterspace0pt
+         \def\nomathspacing{\nulldelimiterspace0pt\mathsurround0pt}
+         $\Bigg( 1 + x\Bigg) \quad \Bigg( \frac{1}{x}\Bigg)$}
+        {\tttf 0pt with reset at end}
+        {\showboxes
+         \nulldelimiterspace10pt
+         \def\nomathspacing{\nulldelimiterspace0pt\mathsurround0pt}
+         $\Bigg( 1 + x\Bigg) \quad \Bigg( \frac{1}{x}\Bigg)$}
+        {\tttf 10pt with reset at end}
+        {\showboxes
+         \nulldelimiterspace10pt
+         \def\nomathspacing{\mathsurround0pt}
+         $\Bigg( 1 + x\Bigg) \quad \Bigg( \frac{1}{x}\Bigg)$}
+        {\tttf 10pt without reset at end}
+    \stopcombination
+\stoplinecorrection
+
+\stopsubject
+
+\startsubject[title=Radicals]
+
+In traditional \TEX\ a radical with degree is defined as macro. That macro does
+some measurements and typesets the result in four sizes for a choice. The macro
+typesets the degree in a box that contains the degree as formula. There is a
+little guesswork going on than with respect to how the radical symbol is shaped
+but as we're talking plain \TEX\ here it works out okay because the default font
+is well known.
+
+Radicals are a nice example of a two dimensional \quote {extender} but only the
+vertical dimension uses the extension mechanism, which itself operates either
+horizontally or vertically, although in principle it could both ways. The
+horizontal extension is a rule and the fact that the shape is below the baseline
+(as are other large symbols) will make the rule connect well: the radical shape
+sticks out a little, so one can think of the height reflecting the rule height.
+\footnote {When you zoom in you will notice that this is of not always optimal
+because of the way the slope touched the rule.} In \OPENTYPE\ fonts there is a
+parameter and in \LUATEX\ we use the default rule thickness for traditional
+fonts, which is correct for Latin Modern. There are more places in the fonts
+where the design relates to this thickness, for instance fraction rules are
+supposed to match the minus, but this is a bit erratic if you compare fonts. This
+is one of the corrections we apply in the goodie files.
+
+In \OPENTYPE\ the specification of the radical also includes spacing properties
+of the degree and that is why we have a primitive in \LUATEX\ that also handles
+the degree. It is what we used in \CONTEXT\ \MKIV. But \unknown\ we actually end
+up with a situation that compares to the already discussed fraction: there is
+space added before a radical when there is a degree. However, because we now have
+a radical atom class, we can avoid using that one and use the new pairwise
+spacing. Some fuzzy spacing logic in the engine could therefore be removed and we
+assume that \type {\Umathradicaldegreebefore} is zero. For the record: the \type
+{\Umathradicaldegreeafter} sort of tells how much space there is above the low
+part of the root, which means that we can compensate for multi|-|digit degrees.
+
+Zeroing a parameter is something that relates to a font which means that it has
+to happen for each math font which in turn can mean a family|-|style combination. In
+order to avoid that complication (or better: to avoid tracing clutter) we have a
+way to disable a parameter:
+
+\startbuffer
+\ruledhbox{$x + \sqrt[123]{b}^1_2$}
+\ruledhbox{$x + \sqrt[12] {b}^1_2$}
+\ruledhbox{$x + \sqrt[1]  {b}^1_2$}
+\ruledhbox{$x + \sqrt     {b}^1_2$}
+\stopbuffer
+
+\typebuffer
+
+\startlinecorrection
+\startcombination[1*4]
+    {\switchtobodyfont[modern]\scale[height=10mm]{\showglyphs\setmathignore\Umathradicaldegreebefore0\getbuffer}}{}
+    {\type {\setmathignore \Umathradicaldegreebefore 0}}{}
+    {\switchtobodyfont[modern]\scale[height=10mm]{\showglyphs\setmathignore\Umathradicaldegreebefore1\getbuffer}}{}
+    {\type {\setmathignore \Umathradicaldegreebefore 1}}{Latin Modern}
+\stopcombination
+\stoplinecorrection
+
+One problem with these spacing parameters is that they are inconsistent across
+fonts. The Latin Modern has a rather large space before the degree, while Cambria
+and Pagella have little. That means that when you prototype a mechanism the
+chosen solution can look great but not so much when at some point you use another
+font.
+
+\startlinecorrection
+\startcombination[1*4]
+    {\switchtobodyfont[pagella]\scale[height=10mm]{\showglyphs\setmathignore\Umathradicaldegreebefore0\getbuffer}}{}
+    {\type {\setmathignore \Umathradicaldegreebefore 0}}{}
+    {\switchtobodyfont[pagella]\scale[height=10mm]{\showglyphs\setmathignore\Umathradicaldegreebefore1\getbuffer}}{}
+    {\type {\setmathignore \Umathradicaldegreebefore 1}}{Cambria}
+\stopcombination
+\stoplinecorrection
+
+\stopsubject
+
+\startsubject[title=More fences]
+
+One of the reasons why the \MKII\ and \MKIV\ fence related mechanism is somewhat
+complex is that we want a clean solution for filtering fences like parenthesis by
+size, something that in the traditional happens via a fake fence pair that
+encapsulates a strut of a certain size. In \LMTX\ we use the same approach but
+have made the sequence more configurable. In practice that means that the values
+1 upto 4 are just that but for some fonts we use the sequence \type {1 3 5 7}.
+There was no need to adapt the engine as it already worked quite well.
+
+\stopsubject
+
+\startsubject[title=Integrals]
+
+The Latin Modern fonts have only one size of big operators and one reason can be
+that there is no need for more. Another reason can be that there was just no
+space in the font. However, an \OPENTYPE\ font has plenty slots available and the
+reference font Cambria has integral signs in sizes as well as extensibles.
+
+In \LUATEX\ we already have generic vertical extensibles but that only works well
+with specified sizes. And, cheating with delimiters has the side effect that we
+get the wrong spacing. In \LUAMETATEX\ however we have ways to adapt the size to
+what came or what comes. In fact, it is a mechanism that is available for any atom
+that we support. However, it doesn't play well with script and this whole \type {\limits}
+and \type {\nolimits} is a bit clumsy so Mikael and I decided that different route had
+to be followed. For adaptive large operators we provide this interface:
+
+\startbuffer[sample-1]
+$ x + \integral [color=darkred,top={t},bottom={b}] {\frac{1}{x}} = 10 $
+\stopbuffer
+
+\startbuffer[sample-2]
+$ x + \startintegral [color=darkblue,top={t},bottom={b}]
+    \frac{1}{x}
+\stopintegral = 10 $
+\stopbuffer
+
+\startbuffer[sample-3]
+$ x + \startintegral [color=darkgreen,top={t},bottom={b},method=vertical]
+    \frac{1}{x}
+\stopintegral= 10 $
+\stopbuffer
+
+\typebuffer [sample-1,sample-2,sample-3]
+
+This text is not about the user interface so we won't discuss how to define additional
+large operators using one|-|liners.
+
+\startlinecorrection
+\startcombination[nx=3,ny=1,distance=2em]
+    {\scale[s=2]{\getbuffer[sample-1]}} {}
+    {\scale[s=2]{\getbuffer[sample-2]}} {}
+    {\scale[s=2]{\getbuffer[sample-3]}} {}
+\stopcombination
+\stoplinecorrection
+
+The low level \LUAMETATEX\ implementation handles this input:
+
+\starttyping
+\Uoperator          \Udelimiter "0 \fam "222B {top} {bottom} {...}
+\Uoperator   limits \Udelimiter "0 \fam "222B {top} {bottom} {...}
+\Uoperator nolimits \Udelimiter "0 \fam "222B {top} {bottom} {...}
+\stoptyping
+
+plus the usual keywords that fenced accept, because after all, this is just a
+special case of fencing.
+
+Currently these special left operators are implemented as a special case of
+fences because that mechanism does the scaling. It means that we need a (bogus)
+right fence, or need to brace the content (basically create an atom). When no
+right fence is found one is added automatically. Because there is no real
+fencing, right fences are removed when processing takes place. When you specify a
+\type {class} that one will be used for the left and right spacing, otherwise we
+have open|/|close spacing.
+
+\stopsubject
+
+\startsubject[title=Going details]
+
+When the next feature was explored Mikael tagged it as math micro typography and
+the reason is that you need not only to set up the engine for it but also need to
+be aware of this kind of spacing. Because we wanted to get rid of this script spacing
+that the font imposes we configured \CONTEXT\ with:
+
+\starttyping
+\setmathignore\Umathspacebeforescript\plusone
+\setmathignore\Umathspaceafterscript \plusone
+\stoptyping
+
+This basically nils all these tiny spaces. But the latest configuration has this
+instead:
+
+\starttyping
+% \setmathignore \Umathspacebeforescript\zerocount % default
+% \setmathignore \Umathspaceafterscript \zerocount % default
+
+\mathslackmode \plusone
+
+\setmathoptions\mathopcode      \plusthree
+\setmathoptions\mathbinarycode  \plusthree
+\setmathoptions\mathrelationcode\plusthree
+\setmathoptions\mathopencode    \plusthree
+\setmathoptions\mathclosecode   \plusthree
+\setmathoptions\mathpunctcode   \plusthree
+\stoptyping
+
+This tells the engine to convert these spaces into what we call slack: disposable
+kerns at the edges. But it also converts these kerns into a glue component when
+possible. As with all these extensions it complicates the machinery but users
+will never see that. Now, the last six lines do the magic that made us return to
+honoring the spaces: we can tell the engine to ignore this slack when there are
+specific classes at the edges. These options are a bitset and \type {1} means
+\quotation {no slack left} and \type {2} means \quotation {no slack right} so
+\type {3} sets both.
+
+\startbuffer
+\def\TestSlack#1%
+  {\vbox\bgroup
+      \mathslackmode\zerocount
+      \hbox\bgroup
+         \setmathignore\Umathspacebeforescript\zerocount
+         \setmathignore\Umathspaceafterscript \zerocount
+         #1
+      \egroup
+      \vskip-.9\lineheight
+      \hbox\bgroup\red
+        \setmathignore\Umathspacebeforescript\plusone
+        \setmathignore\Umathspaceafterscript \plusone
+         #1
+      \egroup
+   \egroup}
+
+\startcombination[nx=3]
+    {\showglyphs\TestSlack{$f^2 >     $}} {}
+    {\showglyphs\TestSlack{$    > f^^2$}} {}
+    {\showglyphs\TestSlack{$f^2 > f^^2$}} {}
+\stopcombination
+\stopbuffer
+
+\typebuffer
+
+\startlinecorrection
+\scale[width=\textwidth]{\getbuffer}
+\stoplinecorrection
+
+Because this overall niling is not granular enough a while later we introduced a
+way to set this per class, as is demonstrated in the next example.
+
+\startbuffer
+\def\TestSlack#1%
+  {\vbox\bgroup
+      \mathslackmode\plusone
+      \hbox\bgroup\red
+        \setmathignore\Umathspacebeforescript\zerocount
+        \setmathignore\Umathspaceafterscript \zerocount
+        #1
+      \egroup
+      \vskip-.9\lineheight
+      \hbox\bgroup\green
+        \setmathoptions\mathrelationcode \zerocount
+        #1
+      \egroup
+      \vskip-.9\lineheight
+      \hbox\bgroup\blue
+        \setmathoptions\mathrelationcode \plusthree
+        #1
+      \egroup
+   \egroup}
+
+\startcombination[nx=3]
+    {\showglyphs\TestSlack{$f^2 >     $}} {}
+    {\showglyphs\TestSlack{$    > f^^2$}} {}
+    {\showglyphs\TestSlack{$f^2 > f^^2$}} {}
+\stopcombination
+\stopbuffer
+
+\typebuffer
+
+\startlinecorrection
+\scale[width=\textwidth]{\getbuffer}
+\stoplinecorrection
+
+Of course we need to experiment a lot with real documents and it might take a
+while before all this is stable (in the engine and in \CONTEXT). And as we don't
+need to conform to the decades old golden \TEX\ math standards we have some
+degrees of freedom in this: for Mikael and me it is pretty much a visual thing
+where we look closely at large samples. Of course in practice details get lost
+when we print at 10 point but that doesn't mean we can't provide the best
+experience. \footnote {Whenever I look at (my) old (math) school books I realize
+that Don Knuth had very good reasons to come up with \TEX\ and, it being hard to
+beat, \TEX\ still sets the standard!}
+
+\stopsubject
+
+\startsubject[title=Ghosts]
+
+As plain \TEX\ has macros like \type {\vphantom} you also find them in macro
+packages that came later. These create a boxes that have their content removed
+after the dimensions are set. They take space and are invisible but there's also
+nothing there.
+
+A variant in the upgraded math machinery are ghosts: these are visible in the
+sense that they show up but ignored when it comes to spacing. Here is an example.
+The option bit set here tells the engine that we ghost at the right, so we have
+ghosts around the relation (it controls where the spacing ends up).
+
+\startbuffer
+$
+  x
+  \mathatom class \mathghostcode                   {!!}
+  >
+  \mathatom class \mathghostcode options "00000020 {!!}
+  1
+  \quad
+  x
+  \mathatom class \mathghostcode                   {\hbox{\smallinfofont ord}}
+  >
+  \mathatom class \mathghostcode options "00000020 {\hbox{\smallinfofont dig}}
+  1
+$
+\stopbuffer
+
+\typebuffer
+
+You never know when this comes in handy but it fits in the new, more granular
+approach to spacing. The code above shows that it's just a class, this time with
+number \number\mathghostcode.
+
+\startlinecorrection
+    \scale[width=\textwidth]{\showglyphs\showmakeup[mathglue]\getbuffer}
+\stoplinecorrection
+
+\stopsubject
+
+\startsubject[title=Struts]
+
+In order to get consistent spacing the \CONTEXT\ macro package makes extensive
+use of struts in text mode as well as math mode. The normal way to implement that is
+either an empty box or a zero width rule, both with a specifically set height
+and depth. In \CONTEXT\ \MKII\ and \MKIV\ (and for a long time in \LMTX\ too) they
+were rules so that we could visualize them: they get some width and kerns
+around them to compensate for that.
+
+In order to not let them interfere with spacing we could wrap them into a ghost
+atom but it is kind of ugly. Anyway, before we had these ghost atoms an
+alternative to struts was already implemented: a special kind of rule. The reason is
+that I wanted a cleaner and more predictable way to adapt struts to the math style
+uses and sometimes predicting that is fragile. What we want is a delayed assignment of
+dimensions.
+
+We have two solutions. The first one uses two math parameters that themselves
+adapt to the style, as do other parameters: \type {\Umathruleheight} and \type
+{\Umathruledepth}. The other solution relates a font (or family) and character
+with the strut rule which is then used as measure for the height and depth. Just
+for the record: this also works in text mode, which is why a recent \LMTX\ also
+does use that for struts now. The optional visualization is just part of the
+regular visualization mechanism in \CONTEXT\ which already had provisions for
+struts. A side effect of this is that the rule primitives now accept three more
+keywords: \type {font}, \type {fam} and \type {char}, in addition to the already
+present traditional ones \type {width}, \type {height} and \type {depth}, the
+(backend) margin ones \type {left} (or \type {top}) and \type {right} (or \type
+{bottom}) options, as well as \type {xoffset} and \type {yoffset}). The command
+that creates a rule with subtype \type {strut} is simply \type {\srule}. Because
+struts are rather macro package specific I leave it to this.
+
+One positive side effect is that we could simplify the \CONTEXT\ fraction mechanism
+a bit. Over time control over the (font driven) gaps was introduced but that is
+not really needed because we zero the gaps anyway. There was also a tolerance
+mechanism which again was not used. However, for skewed fractions we do use the new
+tolerance mechanism as well as gap control.
+
+\stopsubject
+
+\startsubject[title=Atoms]
+
+Now that we have generic atoms (\type {\mathatom}) another, sometimes confusing aspect
+of the math parsing can be solved. Take this:
+
+\starttyping
+\def\MyBin{\mathbin{\tt mybin}}
+$ x ^ \MyBin _ \MyBin $
+\stoptyping
+
+The parser just doesn't like that which means that one has to use
+
+\starttyping
+\def\MyBin{\mathbin{\tt mybin}}
+$ x ^ {\MyBin} _ {\MyBin} $
+\stoptyping
+
+or:
+
+\starttyping
+\def\MyBin{{\mathbin{\tt mybin}}}
+$ x ^ \MyBin _ \MyBin $
+\stoptyping
+
+But the later has side effects: it creates a list that can influence spacing. It
+is for that reason that we do accept atoms where they were not accepted before.
+Of course that itself can have side effects but at least we don't get an error
+message. It fits well into the additional (user) classes model. And, given that
+in \CONTEXT\ the \type {\frac} command is actually wrapped as \type {\mathfrac}
+the next will work too:
+
+\starttyping
+$ x^\frac{1}{2} + x^{\frac{1}{2}} $
+\stoptyping
+
+but in practice you should probably use the braced version here for clarity.
+
+\stopsubject
+
+\startsubject[title=The \type {vcenter} primitive]
+
+Traditionally this primitive is bound to math but it had already be adapted to also
+work in text mode. As part of the upgrade of math we can now also pass all the options
+that normal boxed take and we can also cheat with the axis. Here is an example:
+
+\startbuffer
+\def\TEST{\hbox\bgroup
+    \darkred   \vrule width  2pt height 4pt
+    \darkgreen \vrule width 10pt depth  2pt
+\egroup}
+$
+    x  - \mathatom \mathvcentercode {!!!} -
+    + \ruledvcenter                           {\TEST}
+    + \ruledvcenter                           {\TEST}
+    + \ruledvcenter axis 1                    {\TEST}
+    + \ruledvcenter xoffset  2pt yoffset  2pt {\TEST}
+    + \ruledvcenter xoffset -2pt yoffset -2pt {\TEST}
+    + x
+$
+\stopbuffer
+
+\typebuffer
+
+There was already a vcenter class available before we did this:
+
+\startlinecorrection
+    \scale[width=\textwidth]{\showglyphs\showmakeup[mathglue]\getbuffer}
+\stoplinecorrection
+
+\stopsubject
+
+\startsubject[title=Text]
+
+Sometimes you want text in math, for instance \type {sin} or \type {cos} but
+text in math is not really text:
+
+\startbuffer
+$ \setmathspacing\mathordinarycode\mathordinarycode\textstyle 10mu fin(x) $
+\stopbuffer
+
+\typebuffer
+
+The result demonstrates that what looks like a word actually becomes three
+math atoms:
+
+\startlinecorrection
+    \scale[width=\textwidth]{\showglyphs\showmakeup[mathglue]\getbuffer}
+\stoplinecorrection
+
+Okay, so how about then wrapping it into a text box:
+
+\startbuffer
+$
+    \setmathspacing\mathordinarycode\mathordinarycode\textstyle 10mu
+    fin(x) \quad \hbox{fin}(x)
+$
+\stopbuffer
+
+\typebuffer
+
+Here we get:
+
+\startlinecorrection
+    \scale[width=\textwidth]{\showglyphs\showmakeup[mathglue]\getbuffer}
+\stoplinecorrection
+
+We even get a ligature which might be an indication that we're not using a math
+font which indeed is the case: the box is typeset in the regular text font.
+
+\startbuffer
+\def\Test#1%
+  {\setmathspacing\mathordinarycode\mathordinarycode\textstyle 5mu
+   $\showglyphs
+   #1% style
+   {\tf fin} \quad
+   \hbox{fin} \quad
+   \mathatom class \mathordinarycode textfont {fin}
+   \mathatom class \mathordinarycode textfont {\tf fin}
+   \mathatom class \mathordinarycode textfont {\hbox{fin}}
+   \mathatom class \mathordinarycode mathfont {\hbox{fin}}
+   $}
+\stopbuffer
+
+\typebuffer \getbuffer
+
+When we feed this macro with the \type {\textstyle}, \type {\scriptstyle} and \type
+{\scriptscriptstyle} we get:
+
+\startlinecorrection
+    \startcombination[1*3]
+        {\scale[scale=3000]{\Test\textstyle        }} {text}
+        {\scale[scale=3000]{\Test\scriptstyle      }} {script}
+        {\scale[scale=3000]{\Test\scriptscriptstyle}} {scriptscript}
+    \stopcombination
+\stoplinecorrection
+
+Here you see a new atom option action: \type {textfont} which does as much as
+setting the font to the current family font and the size to the one used in the
+style. For the record: you only get ligatures when they are configured and
+provided by the font (and as math is a script itself it is unlikely to work).
+\footnote {The existing mechanisms in \CONTEXT\ already dealt with this but it is
+nevertheless nice to have it as a clean engine feature.}
+
+\stopsubject
+
+\startsubject[title=Tracing]
+
+I won't discuss the tracing features in \CONTEXT\ here but for sure the
+visualizer helps a lot in figuring out all this. In \LUAMETATEX\ we carry a bit
+more information with the resulting nodes so we can provide more details, for
+instance about the applied spacing and penalties. Some is shown in the examples.
+A more recent tracing feature is this:
+
+\starttyping
+\tracingmath   1
+\tracingonline 1
+$
+    \mathord (
+    \mathord {(}
+    \mathord \Udelimiter"4 0 `(
+    \Udelimiter"4 0 `(
+$
+\stoptyping
+
+That gives us on the console:
+
+\starttyping
+7:3: > \inlinemath=
+7:3: \mathord
+7:3: .\nucleus
+7:3: ..\mathchar (fam="0,char="28)
+7:3: \mathord
+7:3: .\nucleus
+7:3: ..\mathlist
+7:3: ...\mathopen
+7:3: ....\nucleus
+7:3: .....\mathchar (fam="0,char="28)
+7:3: \mathord
+7:3: .\nucleus
+7:3: ..\mathchar (fam="0,char="28)
+7:3: \mathopen
+7:3: .\nucleus
+7:3: ..\mathchar (fam="0,char="28)
+\stoptyping
+
+A tracing level of 2 will spit out some information about applied spacing and
+penalties between atoms (when set) and level 3 will show the math list before the
+first and second pass (a mix of nodes and noads) we well as the result (nodes) plus
+return some details about rules, spacing and penalties applied.
+
+\stopsubject
+
+\startsubject[title=Is there more?]
+
+The engine already provides the option to circumvent the side effect of a change
+in a parameter acting sort of global: the last value given is also the one that a
+second pass starts with. The \type {\frozen} prefix will turn settings into local
+ones but that's another (already old) topic. There are many such improvements and
+options not mentioned here but you can find them mentioned and explained in older
+development stories. A lot has been around for a while but not been applied in
+\CONTEXT\ yet.
+
+When \TEX\ was written one important property (likely related to memory
+consumption) is that node lists have only forward pointers. That means that the
+state of preceding material has to be kept track of: there is no going (or
+looking) back. In \LUATEX\ we have double linked lists so in principle we can try
+to be more clever but so far I decided not to touch the math machinery in that
+way. But who knows what comes next.
+
+\stopsubject
+
+\startsubject[title=Those italics]
+
+Right from the start of \LUATEX\ it became clear that the fact that \TEX\ assumes
+the actual width of glyphs to be incremented by the italic correction that then
+selectively is removed has been an issue. It made for successive attempts to
+improve spacing in \CONTEXT\ by providing pseudo features. But, when we moved
+from assembled \UNICODE\ math fonts to \quote {real} ones that became messy: what
+trick to apply when and even worse where? In the end it are only a very few
+shapes that actually are affected in the sense that when we don't deal with them
+it looks bad. It also happens that one of those shapes is the italic \quote {f},
+a letter that is used frequently in math. It might even be safe to say that the
+simple fact that the math italic f has this excessively wrong width and thereby
+pretty large italic correction is the cause of many problems.
+
+In the \LMTX\ approach Mikael and I settled on patching shapes in the so called
+font goodie files, aka \type {lfg} files and only a handful of entries needed a
+treatment. This makes a good care for removing the traditional font code path
+from \LUAMETATEX.
+
+\startbuffer
+   \dontleavehmode {\tt\fontclass}:
+    \start
+        \showglyphs \setupinterlinespace[1.2]
+        \dostepwiserecurse{`a}{`z}{1}{$\Uchar#1^1_2$ }
+        \dostepwiserecurse{`a}{`z}{1}{$\bi\Uchar#1^1_2$ }
+        \par
+    \stop
+\stopbuffer
+
+\start
+    \switchtobodyfont[modern]  \getbuffer\blank
+    \switchtobodyfont[cambria] \getbuffer\blank
+    \switchtobodyfont[pagella] \getbuffer\blank
+    \switchtobodyfont[termes]  \getbuffer\blank
+    \switchtobodyfont[bonum]   \getbuffer\blank
+\stop
+
+One of the other very sloped symbol is the integral, although most fonts have
+them more upright than tex has. Of course there are many variants of these
+integrals in a math font. Here we also have some font parameters that we can
+tune, which is what we do.
+
+\stopsubject
+
+\startsubject[title=Accents]
+
+Accents are common in languages other than English and it's English that \TEX\
+was made for. Although the seven bit variant became eight bit handling accents
+never was sophisticated and one of the main reasons is of course that one could
+use pre|-|built composed characters. The \OPENTYPE\ format brought proper
+anchoring (aka marks) to font formats and when \LUATEX\ deals with text those
+kick in. In \OPENTYPE\ math however, anchoring is kind of limited to the top
+position only. Because the \TEXGYRE\ fonts are based on traditional \TEX\ fonts,
+their accents have not become better suited.
+
+\startbuffer
+$ \hat{x} \enspace \widehat{x} \enspace \widehat{xx} \enspace \widehat{xxx}
+  \enspace \hat{f} \enspace \widehat{f} $
+\stopbuffer
+
+\typebuffer
+
+When looking at examples you need to be aware of the fact hat fonts can have been
+adapted in the goodie files. \footnote {Extreme examples can be found for Lucida
+Bright where we not only have to fix the extensible parts of horizontal braces
+but also have to provide horizontal brackets.} So, for instance bounding boxes
+and such can differ from the original. Anyway, the previous code in Cambria looks
+as follows.
+
+\startlinecorrection
+\scale[height=18mm]{\showglyphs\switchtobodyfont[cambria]\inlinebuffer}
+\stoplinecorrection
+
+With Latin Modern we get:
+
+\startlinecorrection
+\scale[height=18mm]{\showglyphs\switchtobodyfont[modern]\inlinebuffer}
+\stoplinecorrection
+
+And Dejavu comes out as:
+
+\startlinecorrection
+\scale[height=18mm]{\showglyphs\switchtobodyfont[dejavu]\inlinebuffer}
+\stoplinecorrection
+
+As you can see there are some differences. In for instance Latin Modern the shape
+of the hat and smallest wide hat are different and the first wide one has zero
+dimensions combined with a negative anchor. When an accented character is
+followed by a superscript or prime the italic correction of the base kicks in but
+that cannot be enough to not let this small wide hat overflow into the script. We
+could compensate for it but then we need to know the dimensions. Of course we can
+consult the bounding box but it makes no sense to let heuristics enter the
+machinery here while we're in the process generalization. One option is to have
+two extra parameters that can be used when the width of the accent comes close to
+the width of the base (we then assume that zero accent width means that it has
+base width) we add an additional kern. In the end we settled for a (semi automatic)
+correction option in the goodie files.
+
+There are actually three categories of extensible accents to consider: those that
+resemble the ones used in text (like tildes and hats), those wrapping something
+(like braces and bracket but also arrows) and rules (that in traditional \TEX\
+indeed are rules). In \CONTEXT\ we have different interfaces for each of these
+and in order to have a more extensive control. The text related ones are the
+simplest and closest to what the engine supports out of the box but even there we
+use tweaked glyphs to get better spacing because (of course) fonts have different
+and inconsistent spacing in the boundingbox above and below the real shape. This
+is again some tweak that we moved from being {\em automatic} to being {\em under
+goodie file control}. But this is all too \CONTEXT\ specific to discuss here in
+more detail.
+
+\stopsubject
+
+\startsubject[title=Decision time]
+
+After lots of tests Mikael and I came to the conclusion that we're facing the
+following situation. When typesetting math most single characters are italic and
+we already knew from the start of the \LUATEX\ project that the italics shapes
+are problematic when it comes to typesetting math. But it looks like even some
+upright characters can have italic correction: in TexGyreBonum for instance the
+bold upright \type {f} has italic correction, probably because it then can
+(somehow) kern with a following \type {i}. It anyhow assumes no italic correction
+to be applied between these characters.
+
+In the end the mixed math font model model got more and more stressed so one
+decision was to simply assume fonts to be used that are either Cambria like
+\OPENTYPE, or mostly traditional in metrics, or a hybrid of both. It then made
+more sense to change the engine control options that we have into ones that
+simply enable certain code paths, independent of the fact if a font is \OPENTYPE\
+or not. It then become a bit \quotation {crap in, crap out}, but because we
+already tweak fonts in the goodie files it's quite okay. Some fonts have bad
+metrics anyway or miss characters and it makes no sense to support abandoned
+fonts either. Also, when a traditional font is assembled it one can set up the
+engine with different flags and we can deal with it as we wish. In the end it is
+all up to the macro package to configure things right, which is what we tried to
+do for months when rooting out all the artifacts that fonts bring. \footnote {In
+previous versions one could configure this per font but that has been dropped.}
+
+That said, the reason why some (fuzzy) mixed model works out okay (also in
+\LUATEX) is that proper \OPENTYPE\ fonts use staircase kerns instead of italic
+correction. They also have no ligatures and kerns. We also suspect that not that
+much attention is paid to the rendering. It's a bit like these \quotation {How
+many f's do you count in this sentence?} tests where people tend to overlook
+\type {of}, \type {if} and similar short words. Mathematicians loves \type {f}'s
+but probably also overlook the occasionally weird spacing and kerning.
+
+A side effect is that mixing \OPENTYPE\ and traditional fonts is also no longer
+assumed which in turn made a few (newly introduced) state variables obsolete. Once
+everything is stable (including extensions discussed before) some further cleanup
+can happen. Another side effect is that one needs to tell the engine what to apply
+and where, like this:
+
+\starttyping
+\mathfontcontrol\numexpr \zerocount
+   +\overrulemathcontrolcode
+   +\underrulemathcontrolcode
+   +\fractionrulemathcontrolcode
+   +\radicalrulemathcontrolcode
+   +\accentskewhalfmathcontrolcode
+   +\accentskewapplymathcontrolcode
+ % + checkligatureandkernmathcontrolcode
+   +\applyverticalitalickernmathcontrolcode
+   +\applyordinaryitalickernmathcontrolcode
+   +\staircasekernmathcontrolcode
+ % +\applycharitalickernmathcontrolcode
+ % +\reboxcharitalickernmathcontrolcode
+   +\applyboxeditalickernmathcontrolcode
+   +\applytextitalickernmathcontrolcode
+   +\checktextitalickernmathcontrolcode
+ % +\checkspaceitalickernmathcontrolcode
+   +\applyscriptitalickernmathcontrolcode
+   +\italicshapekernmathcontrolcode
+\relax
+\stoptyping
+
+There might be more control options (also for tracing purposes) and some of the
+symbolic (\CONTEXT) names might change for the better. As usual it will take some
+years before all is stable but because most users use the latest greatest version
+it will be tested well.
+
+After this was decided and effective I also decided to drop the mapping from
+traditional font parameters to the \OPENTYPE\ derives engine ones: we now assume
+that the later are set. After all, we already did that in \CONTEXT\ for the virtual
+assemblies that we started out with in the beginning of \LUATEX\ and \MKIV.
+
+\stopsubject
+
+\startsubject[title=Dirty tricks]
+
+Once you start playing with edge cases you also start wondering if some otherwise
+complex things can be done easier. The next macro brings together a couple of
+features discussed in previous sections. It also uses two state variables:
+\type {\lastleftclass} and \type {\lastrightclass} that hold the most recent
+edge classes.
+
+\startbuffer
+\tolerant\permanent\protected\def\NiceHack[#1]#:#2% special argument parsing
+  {\begingroup
+   \setmathatomrule
+     \mathbegincode\mathbincode % context constants
+     \allmathstyles
+     \mathbegincode\mathbincode
+   \normalexpanded
+     {\setbox\scratchbox\hpack
+        ymove \Umathaxis\Ustyle\mathstyle % an additional box property
+        \bgroup
+          \framed % a context macro
+            [location=middle,#1]
+            {$\Ustyle\mathstyle#2$}%
+        \egroup}%
+   \mathatom
+     class 32 % an unused class
+     \ifnum\lastleftclass <\zerocount\else leftclass  \lastleftclass\fi
+     \ifnum\lastrightclass<\zerocount\else rightclass \lastrightclass\fi
+     \bgroup
+       \box\scratchbox
+     \egroup
+   \endgroup}
+\stopbuffer
+
+\typebuffer \getbuffer
+
+\startbuffer
+\def\MyTest#1%
+  {$              x #1                        x $\quad
+   $              x \NiceHack[offset=0pt]{#1} x $\quad
+   $\displaystyle x #1                        x $\quad
+   $\displaystyle x \NiceHack[offset=0pt]{#1} x $}
+
+\scale[scale=2000]{\MyTest{>}}            \blank
+\scale[scale=2000]{\MyTest{+}}            \blank
+\scale[scale=2000]{\MyTest{!}}            \blank
+\scale[scale=2000]{\MyTest{+\frac{1}{2}+}}\blank
+\scale[scale=2000]{\MyTest{\frac{1}{2}}}  \blank
+\stopbuffer
+
+\typebuffer
+
+Of course this is not code you immediately come up with after reading this text,
+also because you need to know a bit of \CONTEXT.
+
+\startlinecorrection
+\showmakeup[mathglue]\getbuffer
+\stoplinecorrection
+
+\stopsubject
+
+\startsubject[title=Final words]
+
+One can argue that all these new features can make a document look better. But
+you only have to look at what Don Knuth produces himself to see that one always
+could do a good job with \TEX, although maybe at the cost of some extra spacing
+directives. It is the fact that \OPENTYPE\ showed up as we as many more math
+fonts, all with their own (sometimes surprising) special effects, that made us
+adapt the engine. Of course there are also new possibilities that permit better
+and more robust macro support. The \TEX book has a chapter on \quotation {the
+fine points of mathematics typesetting} for a reason.
+
+There has never been an excuse to produce a bad looking documents. It is all
+about care. For sure there is a category of users who are forced to use \TEX, so
+they are excused. There are also those who have no eye for typography and rely on
+the macro package, so there we can to some extent blame the authors of those
+packages. And there are of course the sloppy users, those who don't enter a
+revision loop at all. They could as well use any system that in some way can
+handle math. One can also wonder in what way massive remote editing as well as
+collaborative working on documents make things better. It probably becomes less
+personal. At meetings and platforms \TEX\ users like to bash the alternatives but
+in the end they are part of the same landscape and when it comes to math they
+dominate. Maybe there is less to brawl about then we like: just do your thing and
+try to do it as good as possible. Rely on your eyes and pay attention to the
+details, which is possible because the engine provided the means. The previous
+text shows a few things to pay attention to.
+
+Once all the basics that have to do with proper dimensions, spacing, penalties
+and logic are dealt with, we will move on to the more high level constructs. So,
+expect more.
+
+\stopsubject
+
+% \setdefaultmathcodes
+% $\blackrule\mathatomskip \mathdigitcode \mathdigitcode\textstyle\blackrule$
+
+\stopchapter
+
+\stopcomponent
+
+% \showframe
+%
+% \showmakeup[penalty]
+%
+% \startbuffer
+%     \dorecurse {50} {
+%         test $\darkblue   a +         #1         + b > 2$
+%         test $\darkred    a + b +     #1     + c + d > 2$
+%         test $\darkgreen  a + b + c + #1 + d + e + f > 2$
+%     }
+% \stopbuffer
+%
+% \setuptolerance[verytolerant,stretch]
+%
+% \setuplayout[width=11cm]
+%
+% \starttext
+%     \start
+%         \mathforwardpenalties  0
+%         \mathbackwardpenalties 0
+%         \getbuffer
+%         \par
+%     \stop
+%     \page
+%     \start
+%         \mathforwardpenalties  2 -200 -100
+%         \mathbackwardpenalties 2 -100  -50
+%         \getbuffer
+%         \par
+%     \stop
+%     \page
+%     \start
+%         \mathforwardpenalties  2  200 100
+%         \mathbackwardpenalties 2  100  50
+%         \getbuffer
+%         \par
+%     \stop
+%     \page
+% \stoptext
+
+% example:
+%
+%     $ \left( x + 1 \right )^1_2^^3__4 $
+%     \blank
+%     $ ( x + 1 )^1_2^^3__4 $
+%     \blank
+%     $ (^^3__4 x + 1 )^1_2 $
+
+% example:
+%
+% \registerengineclass[digits][dgs]
+%
+% \newconstant \mathdigitscode \mathdigitscode \mathclassvalue digits
+%
+% \protected\def\mathdigits{\mathatom\mathdigitscode}
+%
+% \copymathspacing \mathdigitscode \mathdigitcode
+%
+% \setmathspacing \mathdigitscode      \mathdigitscode      \allmathstyles 3mu
+% \setmathspacing \mathdigitscode      \mathpunctuationcode \allmathstyles 1mu
+% \setmathspacing \mathpunctuationcode \mathdigitscode      \allmathstyles 1mu
+%
+% \startTEXpage[offset=1dk,width=20dk]
+%     \showboxes\showmakeup[math]
+%     $
+%        x
+%        =
+%        \mathdigits {123}
+%        \mathdigits {456} ,
+%        \mathdigits {78}
+%        =
+%        \mathdigits {123} .
+%        \mathdigits {456} ,
+%        \mathdigits {78}
+%     $
+% \stopTEXpage
+
+% \starttext
+%     \showmakeup[math]
+%     $ x \neq x $ \quad $ x \not x $ \quad $ x \eq\not x $ \quad $ x \not\eq x $\par
+%     \pushoverloadmode
+%     \let\normalnot\not
+%     \permanent\protected\def\not#1{#1\normalnot}
+%     \popoverloadmode
+%     $ x \neq x $ \quad $ x \not x $ \quad $ x \eq\not x $ \quad $ x \not\eq x $\par
+% \stoptext
+
+%     $ \not \eq $\par
+%     $ \eq \not $\par % gets collapsed
+
+% example:  a_1=b_1+c_1 (for spacing)
diff --git a/doc/context/sources/general/manuals/ontarget/ontarget.tex b/doc/context/sources/general/manuals/ontarget/ontarget.tex
index 201ed504e..d6b7ad149 100644
--- a/doc/context/sources/general/manuals/ontarget/ontarget.tex
+++ b/doc/context/sources/general/manuals/ontarget/ontarget.tex
@@ -17,6 +17,7 @@
         \component ontarget-eventually
         \component ontarget-dk
         \component ontarget-anchoring
+        \component ontarget-math
     \stopbodymatter
 
 \stopdocument
diff --git a/doc/context/sources/general/manuals/svg/svg-lmtx.tex b/doc/context/sources/general/manuals/svg/svg-lmtx.tex
index 44fec26cd..38e589b72 100644
--- a/doc/context/sources/general/manuals/svg/svg-lmtx.tex
+++ b/doc/context/sources/general/manuals/svg/svg-lmtx.tex
@@ -7,31 +7,7 @@
 
 % \nopdfcompression
 
-\def\showSVGcode#1#2%
-  {\ctxlua{metapost.showsvgpage{
-        filename = "#1",
-        index    = tonumber(#2),
-        method   = "code"
-    }}}
-
-\def\showSVGcodeG#1#2%
-  {\ctxlua{metapost.showsvgpage{
-        filename = "#1",
-        index    = tonumber(#2),
-        method   = "code",
-        x        = 0,
-        y        = 1000,
-        width    = 1000,
-        height   = 1000,
-        noclip   = true
-    }}}
-
-\def\typeSVGcode#1#2%
-  {\ctxlua{metapost.typesvgpage{
-        filename = "#1",
-        index    = tonumber(#2)
-    }}}
-
+\usemodule[svg]
 \usemodule[abbreviations-logos]
 \usemodule[scite]