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+% language=uk
+
+\environment luatex-style
+\environment luatex-logos
+
+\startcomponent luatex-fonts
+
+\startchapter[reference=fonts,title={Font structure}]
+
+\section {The font tables}
+
+All \TEX\ fonts are represented to \LUA\ code as tables, and internally as
+\CCODE~structures. All keys in the table below are saved in the internal font
+structure if they are present in the table returned by the \type {define_font}
+callback, or if they result from the normal \TFM|/|\VF\ reading routines if there
+is no \type {define_font} callback defined.
+
+The column \quote {\VF} means that this key will be created by the \type
+{font.read_vf()} routine, \quote {\TFM} means that the key will be created by the
+\type {font.read_tfm()} routine, and \quote{used} means whether or not the
+\LUATEX\ engine itself will do something with the key.
+
+The top|-|level keys in the table are as follows:
+
+\starttabulate[|Tl|c|c|c|l|p|]
+\NC \rmbf key \NC \bf vf \NC \bf tfm \NC \bf used \NC \bf value type \NC \bf description \NC \NR
+\NC name             \NC yes \NC yes \NC yes \NC string \NC metric (file) name \NC \NR
+\NC area             \NC no  \NC yes \NC yes \NC string \NC (directory) location, typically empty \NC \NR
+\NC used             \NC no  \NC yes \NC yes \NC boolean\NC indicates usage (initial: false) \NC \NR
+\NC characters       \NC yes \NC yes \NC yes \NC table  \NC the defined glyphs of this font \NC \NR
+\NC checksum         \NC yes \NC yes \NC no  \NC number \NC default: 0 \NC \NR
+\NC designsize       \NC no  \NC yes \NC yes \NC number \NC expected size (default: 655360 == 10pt) \NC \NR
+\NC direction        \NC no  \NC yes \NC yes \NC number \NC default: 0 \NC \NR
+\NC encodingbytes    \NC no  \NC no  \NC yes \NC number \NC default: depends on \type {format} \NC \NR
+\NC encodingname     \NC no  \NC no  \NC yes \NC string \NC encoding name \NC \NR
+\NC fonts            \NC yes \NC no  \NC yes \NC table  \NC locally used fonts \NC \NR
+\NC psname           \NC no  \NC no  \NC yes \NC string \NC This is the \POSTSCRIPT\ fontname in the incoming font
+                                                            source, and it's used as fontname identifier in the \PDF\
+                                                            output. This has to be a valid string, e.g.\ no spaces
+                                                            and such, as the backend will not do a cleanup. This gives
+                                                            complete control to the loader. \NC \NR
+\NC fullname         \NC no  \NC no  \NC yes \NC string \NC output font name, used as a fallback in the \PDF\ output
+                                                            if the \type {psname} is not set \NC \NR
+\NC header           \NC yes \NC no  \NC no  \NC string \NC header comments, if any \NC \NR
+\NC hyphenchar       \NC no  \NC no  \NC yes \NC number \NC default: \TEX's \type {\hyphenchar} \NC \NR
+\NC parameters       \NC no  \NC yes \NC yes \NC hash   \NC default: 7 parameters, all zero \NC \NR
+\NC size             \NC no  \NC yes \NC yes \NC number \NC loaded (at) size. (default: same as designsize) \NC \NR
+\NC skewchar         \NC no  \NC no  \NC yes \NC number \NC default: \TEX's \type {\skewchar} \NC \NR
+\NC type             \NC yes \NC no  \NC yes \NC string \NC basic type of this font \NC \NR
+\NC format           \NC no  \NC no  \NC yes \NC string \NC disk format type \NC \NR
+\NC embedding        \NC no  \NC no  \NC yes \NC string \NC \PDF\ inclusion  \NC \NR
+\NC filename         \NC no  \NC no  \NC yes \NC string \NC the name of the font on disk \NC \NR
+\NC tounicode        \NC no  \NC yes \NC yes \NC number \NC When this is set to~1 \LUATEX\ assumes per|-|glyph
+                                                            tounicode entries are present in the font. \NC \NR
+\NC stretch          \NC no  \NC no  \NC yes \NC number \NC the \quote {stretch} value from \type
+                                                            {\expandglyphsinfont} \NC \NR
+\NC shrink           \NC no  \NC no  \NC yes \NC number \NC the \quote {shrink} value from \type
+                                                            {\expandglyphsinfont} \NC \NR
+\NC step             \NC no  \NC no  \NC yes \NC number \NC the \quote {step} value from \type
+                                                            {\expandglyphsinfont} \NC \NR
+\NC auto_expand      \NC no  \NC no  \NC yes \NC boolean\NC the \quote {autoexpand} keyword from \crlf
+                                                            \type {\expandglyphsinfont} \NC \NR
+\NC expansion_factor \NC no  \NC no  \NC no  \NC number \NC the actual expansion factor of an expanded font \NC \NR
+\NC attributes       \NC no  \NC no  \NC yes \NC string \NC the \type {\pdffontattr} \NC \NR
+\NC cache            \NC no  \NC no  \NC yes \NC string \NC This key controls caching of the \LUA\ table on the
+                                                            \TEX\ end where \type {yes} means: use a reference to
+                                                            the table that is passed to \LUATEX\ (this is the
+                                                            default), and no \type {no} means: don't store the
+                                                            table reference, don't cache any \LUA\ data for this
+                                                            font while \type {renew} means: don't store the table
+                                                            reference, but save a reference to the table that is
+                                                            created at the first access to one of its fields in font.
+                                                            Note: the saved reference is thread|-|local, so be
+                                                            careful when you are using coroutines: an error will be
+                                                            thrown if the table has been cached in one thread, but
+                                                            you reference it from another thread. \NC \NR
+\NC nomath           \NC no  \NC no  \NC yes \NC boolean\NC This key allows a minor speedup for text fonts. If it
+                                                            is present and true, then \LUATEX\ will not check the
+                                                            character entries for math|-|specific keys. \NC \NR
+\NC slant            \NC no  \NC no  \NC yes \NC number \NC This has the same semantics as the \type {SlantFont}
+                                                            operator in font map files. \NC \NR
+\NC extent           \NC no  \NC no  \NC yes \NC number \NC This has the same semantics as the \type {ExtendFont}
+                                                            operator in font map files. \NC \NR
+\stoptabulate
+
+The key \type {name} is always required. The keys \type {stretch}, \type
+{shrink}, \type {step} and optionally \type {auto_expand} only have meaning when
+used together: they can be used to replace a post|-|loading \type
+{\expandglyphsinfont} command. The \type {expansion_factor} is value that can be
+present inside a font in \type {font.fonts}. It is the actual expansion factor (a
+value between \type {-shrink} and \type {stretch}, with step \type {step}) of a
+font that was automatically generated by the font expansion algorithm. The key
+\type {attributes} can be used to set font attributes in the \PDF\ file. The key
+\type {used} is set by the engine when a font is actively in use, this makes sure
+that the font's definition is written to the output file (\DVI\ or \PDF). The
+\TFM\ reader sets it to false. The \type {direction} is a number signalling the
+\quote {normal} direction for this font. There are sixteen possibilities:
+
+\starttabulate[|Tc|Tc|Tc|Tc|]
+\NC \rmbf number \NC \rmbf meaning \NC \rmbf number \NC \rmbf meaning \NC\NR
+\NC 0            \NC LT            \NC  8           \NC TT            \NC\NR
+\NC 1            \NC LL            \NC  9           \NC TL            \NC\NR
+\NC 2            \NC LB            \NC 10           \NC TB            \NC\NR
+\NC 3            \NC LR            \NC 11           \NC TR            \NC\NR
+\NC 4            \NC RT            \NC 12           \NC BT            \NC\NR
+\NC 5            \NC RL            \NC 13           \NC BL            \NC\NR
+\NC 6            \NC RB            \NC 14           \NC BB            \NC\NR
+\NC 7            \NC RR            \NC 15           \NC BR            \NC\NR
+\stoptabulate
+
+These are \OMEGA|-|style direction abbreviations: the first character indicates
+the \quote {first} edge of the character glyphs (the edge that is seen first in
+the writing direction), the second the \quote {top} side. Keep in mind that
+\LUATEX\ has a bit different directional model so these values are not used for
+anything.
+
+The \type {parameters} is a hash with mixed key types. There are seven possible
+string keys, as well as a number of integer indices (these start from 8 up). The
+seven strings are actually used instead of the bottom seven indices, because that
+gives a nicer user interface.
+
+The names and their internal remapping are:
+
+\starttabulate[|lT|c|]
+\NC \rmbf name    \NC \rmbf remapping \NC\NR
+\NC slant         \NC 1 \NC\NR
+\NC space         \NC 2 \NC\NR
+\NC space_stretch \NC 3 \NC\NR
+\NC space_shrink  \NC 4 \NC\NR
+\NC x_height      \NC 5 \NC\NR
+\NC quad          \NC 6 \NC\NR
+\NC extra_space   \NC 7 \NC\LR
+\stoptabulate
+
+The keys \type {type}, \type {format}, \type {embedding}, \type {fullname} and
+\type {filename} are used to embed \OPENTYPE\ fonts in the result \PDF.
+
+The \type {characters} table is a list of character hashes indexed by an integer
+number. The number is the \quote {internal code} \TEX\ knows this character by.
+
+Two very special string indexes can be used also: \type {left_boundary} is a
+virtual character whose ligatures and kerns are used to handle word boundary
+processing. \type {right_boundary} is similar but not actually used for anything
+(yet).
+
+Other index keys are ignored.
+
+Each character hash itself is a hash. For example, here is the character \quote
+{f} (decimal 102) in the font \type {cmr10 at 10pt}:
+
+\starttyping
+[102] = {
+    ['width'] = 200250,
+    ['height'] = 455111,
+    ['depth'] = 0,
+    ['italic'] = 50973,
+    ['kerns'] = {
+        [63] = 50973,
+        [93] = 50973,
+        [39] = 50973,
+        [33] = 50973,
+        [41] = 50973
+    },
+    ['ligatures'] = {
+        [102] = {
+            ['char'] = 11,
+            ['type'] = 0
+        },
+        [108] = {
+            ['char'] = 13,
+            ['type'] = 0
+        },
+        [105] = {
+            ['char'] = 12,
+            ['type'] = 0
+        }
+    }
+}
+\stoptyping
+
+The following top|-|level keys can be present inside a character hash:
+
+\starttabulate[|lT|c|c|c|l|p|]
+\NC \rmbf key \NC \bf vf \NC \bf tfm \NC \bf used \NC \bf type \NC \bf description \NC\NR
+\NC width            \NC yes \NC yes \NC yes   \NC number  \NC character's width, in sp (default 0) \NC\NR
+\NC height           \NC no  \NC yes \NC yes   \NC number  \NC character's height, in sp (default 0) \NC\NR
+\NC depth            \NC no  \NC yes \NC yes   \NC number  \NC character's depth, in sp (default 0) \NC\NR
+\NC italic           \NC no  \NC yes \NC yes   \NC number  \NC character's italic correction, in sp (default zero) \NC\NR
+\NC top_accent       \NC no  \NC no  \NC maybe \NC number  \NC character's top accent alignment place, in sp (default zero) \NC\NR
+\NC bot_accent       \NC no  \NC no  \NC maybe \NC number  \NC character's bottom accent alignment place, in sp (default zero) \NC\NR
+\NC left_protruding  \NC no  \NC no  \NC maybe \NC number  \NC character's \type {\lpcode} \NC\NR
+\NC right_protruding \NC no  \NC no  \NC maybe \NC number  \NC character's \type {\rpcode} \NC\NR
+\NC expansion_factor \NC no  \NC no  \NC maybe \NC number  \NC character's \type {\efcode} \NC\NR
+\NC tounicode        \NC no  \NC no  \NC maybe \NC string  \NC character's \UNICODE\ equivalent(s), in \UTF|-|16BE hexadecimal format \NC\NR
+\NC next             \NC no  \NC yes \NC yes   \NC number  \NC the \quote {next larger} character index \NC\NR
+\NC extensible       \NC no  \NC yes \NC yes   \NC table   \NC the constituent parts of an extensible recipe \NC\NR
+\NC vert_variants    \NC no  \NC no  \NC yes   \NC table   \NC constituent parts of a vertical variant set \NC \NR
+\NC horiz_variants   \NC no  \NC no  \NC yes   \NC table   \NC constituent parts of a horizontal variant set \NC \NR
+\NC kerns            \NC no  \NC yes \NC yes   \NC table   \NC kerning information \NC\NR
+\NC ligatures        \NC no  \NC yes \NC yes   \NC table   \NC ligaturing information \NC\NR
+\NC commands         \NC yes \NC no  \NC yes   \NC array   \NC virtual font commands \NC\NR
+\NC name             \NC no  \NC no  \NC no    \NC string  \NC the character (\POSTSCRIPT) name \NC\NR
+\NC index            \NC no  \NC no  \NC yes   \NC number  \NC the (\OPENTYPE\ or \TRUETYPE) font glyph index \NC\NR
+\NC used             \NC no  \NC yes \NC yes   \NC boolean \NC typeset already (default: false)? \NC\NR
+\NC mathkern         \NC no  \NC no  \NC yes   \NC table   \NC math cut-in specifications \NC\NR
+\stoptabulate
+
+The values of \type {top_accent}, \type {bot_accent} and \type {mathkern} are
+used only for math accent and superscript placement, see the \at {math chapter}
+[math] in this manual for details.
+
+The values of \type {left_protruding} and \type {right_protruding} are used only
+when \type {\protrudechars} is non-zero.
+
+Whether or not \type {expansion_factor} is used depends on the font's global
+expansion settings, as well as on the value of \type {\adjustspacing}.
+
+The usage of \type {tounicode} is this: if this font specifies a \type
+{tounicode=1} at the top level, then \LUATEX\ will construct a \type {/ToUnicode}
+entry for the \PDF\ font (or font subset) based on the character|-|level \type
+{tounicode} strings, where they are available. If a character does not have a
+sensible \UNICODE\ equivalent, do not provide a string either (no empty strings).
+
+If the font level \type {tounicode} is not set, then \LUATEX\ will build up \type
+{/ToUnicode} based on the \TEX\ code points you used, and any character-level
+\type {tounicodes} will be ignored. The string format is exactly the format that
+is expected by Adobe \CMAP\ files (\UTF-16BE in hexadecimal encoding), minus the
+enclosing angle brackets. For instance the \type {tounicode} for a \type {fi}
+ligature would be \type {00660069}. When you pass a number the conversion will be
+done for you.
+
+The presence of \type {extensible} will overrule \type {next}, if that is also
+present. It in in turn can be overruled by \type {vert_variants}.
+
+The \type {extensible} table is very simple:
+
+\starttabulate[|lT|l|p|]
+\NC \rmbf key \NC \bf type \NC \bf description            \NC\NR
+\NC top       \NC number   \NC top character index        \NC\NR
+\NC mid       \NC number   \NC middle character index     \NC\NR
+\NC bot       \NC number   \NC bottom character index     \NC\NR
+\NC rep       \NC number   \NC repeatable character index \NC\NR
+\stoptabulate
+
+The \type {horiz_variants} and \type {vert_variants} are arrays of components.
+Each of those components is itself a hash of up to five keys:
+
+\starttabulate[|lT|l|p|]
+\NC \rmbf key \NC \bf type \NC \bf explanation \NC\NR
+\NC glyph     \NC number   \NC The character index. Note that this is an encoding number, not a name. \NC \NR
+\NC extender  \NC number   \NC One (1) if this part is repeatable, zero (0) otherwise. \NC \NR
+\NC start     \NC number   \NC The maximum overlap at the starting side (in scaled points). \NC \NR
+\NC end       \NC number   \NC The maximum overlap at the ending side (in scaled points). \NC \NR
+\NC advance   \NC number   \NC The total advance width of this item. It can be zero or missing,
+                               then the natural size of the glyph for character \type {component}
+                               is used. \NC \NR
+\stoptabulate
+
+The \type {kerns} table is a hash indexed by character index (and \quote
+{character index} is defined as either a non|-|negative integer or the string
+value \type {right_boundary}), with the values the kerning to be applied, in
+scaled points.
+
+The \type {ligatures} table is a hash indexed by character index (and \quote
+{character index} is defined as either a non|-|negative integer or the string
+value \type {right_boundary}), with the values being yet another small hash, with
+two fields:
+
+\starttabulate[|lT|l|p|]
+\NC \rmbf key \NC \bf type \NC \bf description \NC \NR
+\NC type      \NC number   \NC the type of this ligature command, default 0 \NC \NR
+\NC char      \NC number   \NC the character index of the resultant ligature \NC \NR
+\stoptabulate
+
+The \type {char} field in a ligature is required.
+
+The \type {type} field inside a ligature is the numerical or string value of one
+of the eight possible ligature types supported by \TEX. When \TEX\ inserts a new
+ligature, it puts the new glyph in the middle of the left and right glyphs. The
+original left and right glyphs can optionally be retained, and when at least one
+of them is kept, it is also possible to move the new \quote {insertion point}
+forward one or two places. The glyph that ends up to the right of the insertion
+point will become the next \quote {left}.
+
+\starttabulate[|l|c|l|l|]
+\NC \bf textual (Knuth)   \NC \bf number \NC \bf string   \NC result       \NC\NR
+\NC \type{l + r =: n}     \NC 0          \NC \type{=:}     \NC \type{|n}   \NC\NR
+\NC \type{l + r =:| n}    \NC 1          \NC \type{=:|}    \NC \type{|nr}  \NC\NR
+\NC \type{l + r |=: n}    \NC 2          \NC \type{|=:}    \NC \type{|ln}  \NC\NR
+\NC \type{l + r |=:| n}   \NC 3          \NC \type{|=:|}   \NC \type{|lnr} \NC\NR
+\NC \type{l + r  =:|> n}  \NC 5          \NC \type{=:|>}   \NC \type{n|r}  \NC\NR
+\NC \type{l + r |=:> n}   \NC 6          \NC \type{|=:>}   \NC \type{l|n}  \NC\NR
+\NC \type{l + r |=:|> n}  \NC 7          \NC \type{|=:|>}  \NC \type{l|nr} \NC\NR
+\NC \type{l + r |=:|>> n} \NC 11         \NC \type{|=:|>>} \NC \type{ln|r} \NC\NR
+\stoptabulate
+
+The default value is~0, and can be left out. That signifies a \quote {normal}
+ligature where the ligature replaces both original glyphs. In this table the~\type {|}
+indicates the final insertion point.
+
+The \type {commands} array is explained below.
+
+\section {Real fonts}
+
+Whether or not a \TEX\ font is a \quote {real} font that should be written to the
+\PDF\ document is decided by the \type {type} value in the top|-|level font
+structure. If the value is \type {real}, then this is a proper font, and the
+inclusion mechanism will attempt to add the needed font object definitions to the
+\PDF. Values for \type {type} are:
+
+\starttabulate[|Tl|p|]
+\NC \rmbf value \NC \rmbf description      \NC\NR
+\NC real        \NC this is a base font    \NC\NR
+\NC virtual     \NC this is a virtual font \NC\NR
+\stoptabulate
+
+The actions to be taken depend on a number of different variables:
+
+\startitemize[packed]
+\startitem
+    Whether the used font fits in an 8-bit encoding scheme or not.
+\stopitem
+\startitem
+    The type of the disk font file.
+\stopitem
+\startitem
+    The level of embedding requested.
+\stopitem
+\stopitemize
+
+A font that uses anything other than an 8-bit encoding vector has to be written
+to the \PDF\ in a different way.
+
+The rule is: if the font table has \type {encodingbytes} set to~2, then this is a
+wide font, in all other cases it isn't. The value~2 is the default for \OPENTYPE\
+and \TRUETYPE\ fonts loaded via \LUA. For \TYPEONE\ fonts, you have to set \type
+{encodingbytes} to~2 explicitly. For \PK\ bitmap fonts, wide font encoding is not
+supported at all.
+
+If no special care is needed, \LUATEX\ currently falls back to the
+mapfile|-|based solution used by \PDFTEX\ and \DVIPS. This behaviour might
+silently be removed in the future, in which case the related primitives and \LUA\
+functions will become no|-|ops.
+
+If a \quote {wide} font is used, the new subsystem kicks in, and some
+extra fields have to be present in the font structure. In this case, \LUATEX\
+does not use a map file at all.
+
+The extra fields are: \type {format}, \type {embedding}, \type {fullname}, \type
+{cidinfo} (as explained above), \type {filename}, and the \type {index} key in
+the separate characters.
+
+Values for \type {format} are:
+
+\starttabulate[|Tl|p|]
+\NC \rmbf value \NC \rmbf description                                         \NC \NR
+\NC type1       \NC this is a \POSTSCRIPT\ \TYPEONE\ font                     \NC \NR
+\NC type3       \NC this is a bitmapped (\PK) font                            \NC \NR
+\NC truetype    \NC this is a \TRUETYPE\ or \TRUETYPE|-|based \OPENTYPE\ font \NC \NR
+\NC opentype    \NC this is a \POSTSCRIPT|-|based \OPENTYPE\ font             \NC \NR
+\stoptabulate
+
+\type {type3} fonts are provided for backward compatibility only, and do not
+support the new wide encoding options.
+
+Values for \type {embedding} are:
+
+\starttabulate[|Tl|p|]
+\NC \rmbf value \NC \rmbf description                       \NC \NR
+\NC no          \NC don't embed the font at all             \NC \NR
+\NC subset      \NC include and atttempt to subset the font \NC \NR
+\NC full        \NC include this font in its entirety       \NC \NR
+\stoptabulate
+
+The other fields are used as follows: The \type {fullname} will be the
+\POSTSCRIPT|/|\PDF\ font name. The \type {cidinfo} will be used as the character
+set (the CID \type {/Ordering} and \type {/Registry} keys). The \type {filename}
+points to the actual font file. If you include the full path in the \type
+{filename} or if the file is in the local directory, \LUATEX\ will run a little
+bit more efficient because it will not have to re|-|run the \type {find_xxx_file}
+callback in that case.
+
+Be careful: when mixing old and new fonts in one document, it is possible to
+create \POSTSCRIPT\ name clashes that can result in printing errors. When this
+happens, you have to change the \type {fullname} of the font.
+
+Typeset strings are written out in a wide format using 2~bytes per glyph, using
+the \type {index} key in the character information as value. The overall effect
+is like having an encoding based on numbers instead of traditional (\POSTSCRIPT)
+name|-|based reencoding. The way to get the correct \type {index} numbers for
+\TYPEONE\ fonts is by loading the font via \type {fontloader.open} and use the table
+indices as \type {index} fields.
+
+In order to make sure that cut and paste of the final document works okay you can
+best make sure that there is a \type {tounicode} vector enforced.
+
+\section[virtualfonts]{Virtual fonts}
+
+\subsection{The structure}
+
+You have to take the following steps if you want \LUATEX\ to treat the returned
+table from \type {define_font} as a virtual font:
+
+\startitemize[packed]
+\startitem
+    Set the top|-|level key \type {type} to \type {virtual}.
+\stopitem
+\startitem
+    Make sure there is at least one valid entry in \type {fonts} (see below).
+\stopitem
+\startitem
+    Give a \type {commands} array to every character (see below).
+\stopitem
+\stopitemize
+
+The presence of the toplevel \type {type} key with the specific value \type
+{virtual} will trigger handling of the rest of the special virtual font fields in
+the table, but the mere existence of 'type' is enough to prevent \LUATEX\ from
+looking for a virtual font on its own.
+
+Therefore, this also works \quote {in reverse}: if you are absolutely certain
+that a font is not a virtual font, assigning the value \type {base} or \type
+{real} to \type {type} will inhibit \LUATEX\ from looking for a virtual font
+file, thereby saving you a disk search.
+
+The \type {fonts} is another \LUA\ array. The values are one- or two|-|key
+hashes themselves, each entry indicating one of the base fonts in a virtual font.
+In case your font is referring to itself, you can use the \type {font.nextid()}
+function which returns the index of the next to be defined font which is probably
+the currently defined one.
+
+An example makes this easy to understand
+
+\starttyping
+fonts = {
+    { name = 'ptmr8a', size = 655360 },
+    { name = 'psyr', size = 600000 },
+    { id = 38 }
+}
+\stoptyping
+
+says that the first referenced font (index 1) in this virtual font is \type
+{ptrmr8a} loaded at 10pt, and the second is \type {psyr} loaded at a little over
+9pt. The third one is previously defined font that is known to \LUATEX\ as font id
+\quote {38}.
+
+The array index numbers are used by the character command definitions that are
+part of each character.
+
+The \type {commands} array is a hash where each item is another small array,
+with the first entry representing a command and the extra items being the
+parameters to that command. The allowed commands and their arguments are:
+
+\starttabulate[|Tl|l|l|p|]
+\NC \rmbf command name \NC \bf arguments \NC \bf type \NC \bf description \NC\NR
+\NC font    \NC 1   \NC number    \NC select a new font from the local \type {fonts} table\NC\NR
+\NC char    \NC 1   \NC number    \NC typeset this character number from the current font,
+                                      and move right by the character's width\NC\NR
+\NC node    \NC 1   \NC node      \NC output this node (list), and move right
+                                      by the width of this list\NC\NR
+\NC slot    \NC 2   \NC number    \NC a shortcut for the combination of a font and char command\NC\NR
+\NC push    \NC 0   \NC           \NC save current position\NC\NR
+\NC nop     \NC 0   \NC           \NC do nothing \NC\NR
+\NC pop     \NC 0   \NC           \NC pop position \NC\NR
+\NC rule    \NC 2   \NC 2 numbers \NC output a rule $ht*wd$, and move right.\NC\NR
+\NC down    \NC 1   \NC number    \NC move down on the page\NC\NR
+\NC right   \NC 1   \NC number    \NC move right on the page\NC\NR
+\NC special \NC 1   \NC string    \NC output a \type {\special} command\NC\NR
+\NC lua     \NC 1   \NC string    \NC execute a \LUA\ script (at \type {\latelua} time)\NC\NR
+\NC image   \NC 1   \NC image     \NC output an image (the argument can be either an \type
+                                      {<image>} variable or an \type {image_spec} table)\NC\NR
+\NC comment \NC any \NC any       \NC the arguments of this command are ignored\NC\NR
+\stoptabulate
+
+When a font id is set to~0 then it will be replaced by the currently assigned
+font id. This prevents the need for hackery with future id's (normally one could
+use \type {font.nextid} but when more complex fonts are built in the meantime
+other instances could have been loaded.
+
+Here is a rather elaborate glyph commands example:
+
+\starttyping
+...
+commands = {
+    { 'push' },                    -- remember where we are
+    { 'right', 5000 },             -- move right about 0.08pt
+    { 'font', 3 },                 -- select the fonts[3] entry
+    { 'char', 97 },                -- place character 97 (ASCII 'a')
+    { 'pop' },                     -- go all the way back
+    { 'down', -200000 },           -- move upwards by about 3pt
+    { 'special', 'pdf: 1 0 0 rg' } -- switch to red color
+    { 'rule', 500000, 20000 }      -- draw a bar
+    { 'special','pdf: 0 g' }       -- back to black
+}
+...
+\stoptyping
+
+The default value for \type {font} is always~1 at the start of the
+\type {commands} array. Therefore, if the virtual font is essentially only a
+re|-|encoding, then you do usually not have create an explicit \quote {font}
+command in the array.
+
+Rules inside of \type {commands} arrays are built up using only two dimensions:
+they do not have depth. For correct vertical placement, an extra \type {down}
+command may be needed.
+
+Regardless of the amount of movement you create within the \type {commands}, the
+output pointer will always move by exactly the width that was given in the \type
+{width} key of the character hash. Any movements that take place inside the \type
+{commands} array are ignored on the upper level.
+
+\subsection{Artificial fonts}
+
+Even in a \quote {real} font, there can be virtual characters. When \LUATEX\
+encounters a \type {commands} field inside a character when it becomes time to
+typeset the character, it will interpret the commands, just like for a true
+virtual character. In this case, if you have created no \quote {fonts} array,
+then the default (and only) \quote {base} font is taken to be the current font
+itself. In practice, this means that you can create virtual duplicates of
+existing characters which is useful if you want to create composite characters.
+
+Note: this feature does {\it not\/} work the other way around. There can not be
+\quote {real} characters in a virtual font! You cannot use this technique for
+font re-encoding either; you need a truly virtual font for that (because
+characters that are already present cannot be altered).
+
+\subsection{Example virtual font}
+
+Finally, here is a plain \TEX\ input file with a virtual font demonstration:
+
+\startbuffer
+\directlua {
+  callback.register('define_font',
+    function (name,size)
+      if name == 'cmr10-red' then
+        f = font.read_tfm('cmr10',size)
+        f.name = 'cmr10-red'
+        f.type = 'virtual'
+        f.fonts = {{ name = 'cmr10', size = size }}
+        for i,v in pairs(f.characters) do
+          if (string.char(i)):find('[tacohanshartmut]') then
+             v.commands = {
+               {'special','pdf: 1 0 0 rg'},
+               {'char',i},
+               {'special','pdf: 0 g'},
+              }
+          else
+             v.commands = {{'char',i}}
+          end
+        end
+      else
+        f = font.read_tfm(name,size)
+      end
+      return f
+    end
+  )
+}
+
+\font\myfont = cmr10-red at 10pt \myfont  This is a line of text \par
+\font\myfontx= cmr10     at 10pt \myfontx Here is another line of text \par
+\stopbuffer
+
+\typebuffer
+
+\section{The \type {font} library}
+
+The font library provides the interface into the internals of the font system,
+and also it contains helper functions to load traditional \TEX\ font metrics
+formats. Other font loading functionality is provided by the \type {fontloader}
+library that will be discussed in the next section.
+
+\subsection{Loading a \TFM\ file}
+
+The behavior documented in this subsection is considered stable in the sense that
+there will not be backward-incompatible changes any more.
+
+\startfunctioncall
+<table> fnt =
+    font.read_tfm(<string> name, <number> s)
+\stopfunctioncall
+
+The number is a bit special:
+
+\startitemize
+\startitem
+    If it is positive, it specifies an \quote {at size} in scaled points.
+\stopitem
+\startitem
+    If it is negative, its absolute value represents a \quote {scaled}
+    setting relative to the designsize of the font.
+\stopitem
+\stopitemize
+
+The internal structure of the metrics font table that is returned is explained in
+\in {chapter} [fonts].
+
+\subsection{Loading a \VF\ file}
+
+The behavior documented in this subsection is considered stable in the sense that
+there will not be backward-incompatible changes any more.
+
+\startfunctioncall
+<table> vf_fnt =
+    font.read_vf(<string> name, <number> s)
+\stopfunctioncall
+
+The meaning of the number \type {s} and the format of the returned table are
+similar to the ones in the \type {read_tfm()} function.
+
+\subsection{The fonts array}
+
+The whole table of \TEX\ fonts is accessible from \LUA\ using a virtual array.
+
+\starttyping
+font.fonts[n] = { ... }
+<table> f = font.fonts[n]
+\stoptyping
+
+See \in {chapter} [fonts] for the structure of the tables. Because this is a
+virtual array, you cannot call \type {pairs} on it, but see below for the \type
+{font.each} iterator.
+
+The two metatable functions implementing the virtual array are:
+
+\startfunctioncall
+<table> f = font.getfont(<number> n)
+font.setfont(<number> n, <table> f)
+\stopfunctioncall
+
+Note that at the moment, each access to the \type {font.fonts} or call to \type
+{font.getfont} creates a \LUA\ table for the whole font. This process can be quite
+slow. In a later version of \LUATEX, this interface will change (it will start
+using userdata objects instead of actual tables).
+
+Also note the following: assignments can only be made to fonts that have already
+been defined in \TEX, but have not been accessed {\it at all\/} since that
+definition. This limits the usability of the write access to \type {font.fonts}
+quite a lot, a less stringent ruleset will likely be implemented later.
+
+\subsection{Checking a font's status}
+
+You can test for the status of a font by calling this function:
+
+\startfunctioncall
+<boolean> f =
+    font.frozen(<number> n)
+\stopfunctioncall
+
+The return value is one of \type {true} (unassignable), \type {false} (can be
+changed) or \type {nil} (not a valid font at all).
+
+\subsection{Defining a font directly}
+
+You can define your own font into \type {font.fonts} by calling this function:
+
+\startfunctioncall
+<number> i =
+    font.define(<table> f)
+\stopfunctioncall
+
+The return value is the internal id number of the defined font (the index into
+\type {font.fonts}). If the font creation fails, an error is raised. The table
+is a font structure, as explained in \in {chapter} [fonts].
+
+\subsection{Projected next font id}
+
+\startfunctioncall
+<number> i =
+    font.nextid()
+\stopfunctioncall
+
+This returns the font id number that would be returned by a \type {font.define}
+call if it was executed at this spot in the code flow. This is useful for virtual
+fonts that need to reference themselves.
+
+\subsection{Font id}
+
+\startfunctioncall
+<number> i =
+    font.id(<string> csname)
+\stopfunctioncall
+
+This returns the font id associated with \type {csname} string, or $-1$ if \type
+{csname} is not defined.
+
+\subsection{Currently active font}
+
+\startfunctioncall
+<number> i = font.current()
+font.current(<number> i)
+\stopfunctioncall
+
+This gets or sets the currently used font number.
+
+\subsection{Maximum font id}
+
+\startfunctioncall
+<number> i =
+    font.max()
+\stopfunctioncall
+
+This is the largest used index in \type {font.fonts}.
+
+\subsection{Iterating over all fonts}
+
+\startfunctioncall
+for i,v in font.each() do
+  ...
+end
+\stopfunctioncall
+
+This is an iterator over each of the defined \TEX\ fonts. The first returned
+value is the index in \type {font.fonts}, the second the font itself, as a \LUA\
+table. The indices are listed incrementally, but they do not always form an array
+of consecutive numbers: in some cases there can be holes in the sequence.
+
+\stopchapter
+
+\stopcomponent