Merge pull request #228 from phi-gamma/master

merge version 2.5 (texlive2014) into master

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+%% Copyright (C) 2009-2014
+%%
+%%      by  Elie Roux      <elie.roux@telecom-bretagne.eu>
+%%      and Khaled Hosny   <khaledhosny@eglug.org>
+%%      and Philipp Gesang <philipp.gesang@alumni.uni-heidelberg.de>
+%%
+%% This file is part of Luaotfload.
+%%
+%%      Home:      https://github.com/lualatex/luaotfload
+%%      Support:   <lualatex-dev@tug.org>.
+%%
+%% Luaotfload is under the GPL v2.0 (exactly) license.
+%%
+%% ----------------------------------------------------------------------------
+%%
+%% Luaotfload is free software; you can redistribute it and/or
+%% modify it under the terms of the GNU General Public License
+%% as published by the Free Software Foundation; version 2
+%% of the License.
+%%
+%% Luaotfload is distributed in the hope that it will be useful,
+%% but WITHOUT ANY WARRANTY; without even the implied warranty of
+%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+%% GNU General Public License for more details.
+%%
+%% You should have received a copy of the GNU General Public License
+%% along with Luaotfload; if not, see <http://www.gnu.org/licenses/>.
+%%
+%% ----------------------------------------------------------------------------
+%%
+
+\beginfrontmatter
+
+  \setdocumenttitle  {The \identifier{luaotfload} package}
+  \setdocumentdate   {2014/**/** v2.5}
+  \setdocumentauthor {Elie Roux · Khaled Hosny · Philipp Gesang\\
+                      Home:    \hyperlink {https://github.com/lualatex/luaotfload}\\
+                      Support: \email     {lualatex-dev@tug.org}}
+
+  \typesetdocumenttitle
+
+  \beginabstractcontent
+    This package is an adaptation of the \CONTEXT font loading system.
+    It allows for loading \OpenType fonts with an extended syntax and adds
+    support for a variety of font features.
+  \endabstractcontent
+
+\endfrontmatter
+
+\typesetcontent
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Introduction}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+Font management and installation has always been painful with \TEX.  A
+lot of files are needed for one font (\abbrev{tfm}, \abbrev{pfb},
+\abbrev{map}, \abbrev{fd}, \abbrev{vf}), and due to the 8-Bit encoding
+each font is limited to 256 characters.
+
+But the font world has evolved since the original \TEX, and new
+typographic systems have appeared, most notably the so called
+\emphasis{smart font} technologies like \OpenType fonts (\abbrev{otf}).
+
+These fonts can contain many more characters than \TEX fonts, as well
+as additional functionality like ligatures, old-style numbers, small
+capitals, etc., and support more complex writing systems like Arabic
+and Indic\footnote{%
+  Unfortunately, \identifier{luaotfload} doesn‘t support many Indic
+  scripts right now.
+  Assistance in implementing the prerequisites is greatly
+  appreciated.
+}
+scripts.
+
+\OpenType fonts are widely deployed and available for all modern
+operating systems.
+
+As of 2013 they have become the de facto standard for advanced text
+layout.
+
+However, until recently the only way to use them directly in the \TEX
+world was with the \XETEX engine.
+
+Unlike \XETEX, \LUATEX has no built-in support for \OpenType or
+technologies other than the original \TEX fonts.
+
+Instead, it provides hooks for executing \LUA code during the \TEX run
+that allow implementing extensions for loading fonts and manipulating
+how input text is processed without modifying the underlying engine.
+
+This is where \identifier{luaotfload} comes into play:
+Based on code from \CONTEXT, it extends \LUATEX with functionality necessary
+for handling \OpenType fonts.
+
+Additionally, it provides means for accessing fonts known to the operating
+system conveniently by indexing the metadata.
+
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Thanks}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\identifier{Luaotfload} is part of \LUALATEX, the community-driven
+project to provide a foundation for using the \LATEX format with the
+full capabilites of the \LUATEX engine.
+%
+As such, the distinction between end users, contributors, and project
+maintainers is intentionally kept less strict, lest we unduly
+personalize the common effort.
+
+Nevertheless, the current maintainers would like to express their
+gratitude to Khaled Hosny, Akira Kakuto, Hironori Kitagawa and Dohyun
+Kim.
+%
+Their contributions -- be it patches, advice, or systematic
+testing -- made the switch from version 1.x to 2.2 possible.
+%
+Also, Hans Hagen, the author of the font loader, made porting the
+code to \LATEX a breeze due to the extra effort he invested into
+isolating it from the rest of \CONTEXT, not to mention his assistance
+in the task and willingness to respond to our suggestions.
+
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Loading Fonts}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\identifier{luaotfload} supports an extended font request syntax:
+
+\beginnarrower
+      \nonproportional{\string\font\string\foo\space= \string{}%
+      \meta{prefix}\nonproportional{:}%
+      \meta{font name}\nonproportional{:}%
+      \meta{font features}\nonproportional{\string}}%
+      \meta{\TEX font features}
+\endnarrower
+
+\noindent
+The curly brackets are optional and escape the spaces in the enclosed
+font name.
+%
+Alternatively, double quotes serve the same purpose.
+%
+A selection of individual parts of the syntax are discussed below;
+for a more formal description see figure \ref{font-syntax}.
+
+\beginsyntaxfloat
+  {font-syntax}
+  {Font request syntax.
+   Braces or double quotes around the
+   \emphasis{specification} rule will
+   preserve whitespace in file names.
+   In addition to the font style modifiers
+   (\emphasis{slash-notation}) given above, there
+   are others that are recognized but will be silently
+   ignored: \nonproportional{aat},
+            \nonproportional{icu}, and
+            \nonproportional{gr}.
+   The special terminals are:
+   \smallcaps {feature\textunderscore id} for a valid font
+      feature name and
+   \smallcaps {feature\textunderscore value} for the corresponding
+      value.
+   \smallcaps {tfmname} is the name of a \abbrev{tfm} file.
+   \smallcaps {digit}  again refers to bytes 48--57, and
+   \smallcaps {all\textunderscore characters} to all byte values.
+   \smallcaps {csname} and \smallcaps {dimension} are the \TEX concepts.}
+%
+      <definition>      ::= `\\font', {\sc csname}, `=', <font request>, [ <size> ] ;
+
+      <size>            ::= `at', {\sc dimension} ;
+
+      <font request>    ::= `"', <unquoted font request> `"'
+      \alt                  `{', <unquoted font request> `}'
+      \alt                  <unquoted font request> ;
+
+      <unquoted font request> ::= <specification>, [`:', <feature list> ]
+      \alt                        `[', <path lookup> `]', [ [`:'], <feature list> ] ;
+
+      <specification>    ::= <prefixed spec>, [ <subfont no> ], \{ <modifier> \}
+      \alt                   <anon lookup>, \{ <modifier> \} ;
+
+      <prefixed spec>    ::= `file:', <file lookup>
+      \alt                   `name:', <name lookup> ;
+
+      <file lookup>      ::= \{ <name character> \} ;
+
+      <name lookup>      ::= \{ <name character> \} ;
+
+      <anon lookup>      ::= {\sc tfmname} | <name lookup> ;
+
+      <path lookup>      ::= \{ {\sc all_characters} - `]' \} ;
+
+      <modifier>         ::= `/', (`I' | `B' | `BI' | `IB' | `S=', \{ {\sc digit} \} ) ;
+
+      <subfont no>       ::= `(', \{ {\sc digit} \}, `)' ;
+
+      <feature list>     ::= <feature expr>, \{ `;', <feature expr> \} ;
+
+      <feature expr>     ::= {\sc feature_id}, `=', {\sc feature_value}
+      \alt                   <feature switch>, {\sc feature_id} ;
+
+      <feature switch>   ::= `+' | `-' ;
+
+      <name character>   ::= {\sc all_characters} - ( `(' | `/' | `:' ) ;
+\endsyntaxfloat
+
+\beginsubsection{Prefix -- the \identifier{luaotfload}{ }Way}
+
+In \identifier{luaotfload}, the canonical syntax for font requests
+requires a \emphasis{prefix}:
+%
+\beginnarrower
+  \nonproportional{\string\font\string\fontname\space= }%
+  \meta{prefix}%
+  \nonproportional{:}%
+  \meta{fontname}%
+  \dots
+\endnarrower
+%
+where \meta{prefix} is either \inlinecode{file:} or \inlinecode {name:}.\footnote{%
+  The development version also knows two further prefixes,
+  \inlinecode {kpse:} and \inlinecode {my:}.
+  %
+  A \inlinecode {kpse} lookup is restricted to files that can be found by
+  \identifier{kpathsea} and
+  will not attempt to locate system fonts.
+  %
+  This behavior can be of value when an extra degree of encapsulation is
+  needed, for instance when supplying a customized tex distribution.
+
+  The \inlinecode {my} lookup takes this a step further: it lets you define
+  a custom resolver function and hook it into the \luafunction{resolve_font}
+  callback.
+  %
+  This ensures full control over how a file is located.
+  %
+  For a working example see the
+  \hyperlink [test repo]{https://bitbucket.org/phg/lua-la-tex-tests/src/5f6a535d/pln-lookup-callback-1.tex}.
+}
+%
+It determines whether the font loader should interpret the request as
+a \emphasis{file name} or
+  \emphasis{font name}, respectively,
+which again influences how it will attempt to locate the font.
+%
+Examples for font names are
+            “Latin Modern Italic”,
+            “GFS Bodoni Rg”, and
+            “PT Serif Caption”
+-- they are the human readable identifiers
+usually listed in drop-down menus and the like.\footnote{%
+  Font names may appear like a great choice at first because they
+  offer seemingly more intuitive identifiers in comparison to arguably
+  cryptic file names:
+  %
+  “PT Sans Bold” is a lot more descriptive than \fileent{PTS75F.ttf}.
+  On the other hand, font names are quite arbitrary and there is no
+  universal method to determine their meaning.
+  %
+  While \identifier{luaotfload} provides fairly sophisticated heuristic
+  to figure out a matching font style, weight, and optical size, it
+  cannot be relied upon to work satisfactorily for all font files.
+  %
+  For an in-depth analysis of the situation and how broken font names
+  are, please refer to
+  \hyperlink [this post]{http://www.ntg.nl/pipermail/ntg-context/2013/073889.html}
+  by Hans Hagen, the author of the font loader.
+  %
+  If in doubt, use filenames.
+  %
+  \fileent{luaotfload-tool} can perform the matching for you with the
+  option \inlinecode {--find=<name>}, and you can use the file name it returns
+  in your font definition.
+}
+%
+In order for fonts installed both in system locations and in your
+\fileent{texmf} to be accessible by font name, \identifier{luaotfload} must
+first collect the metadata included in the files.
+%
+Please refer to section~\ref{sec:fontdb} below for instructions on how to
+create the database.
+
+File names are whatever your file system allows them to be, except
+that that they may not contain the characters
+  \inlinecode {(},
+  \inlinecode {:}, and
+  \inlinecode {/}.
+%
+As is obvious from the last exception, the \inlinecode {file:} lookup will
+not process paths to the font location -- only those
+files found when generating the database are addressable this way.
+%
+Continue below in the \XETEX section if you need to load your fonts
+by path.
+%
+The file names corresponding to the example font names above are
+  \fileent{lmroman12-italic.otf},
+  \fileent{GFSBodoni.otf}, and
+  \fileent{PTZ56F.ttf}.
+
+\endsubsection
+
+\beginsubsection {Compatibility Layer}
+
+In addition to the regular prefixed requests, \identifier{luaotfload}
+accepts loading fonts the \XETEX way.
+%
+There are again two modes: bracketed and unbracketed.
+A bracketed request looks as follows.
+
+\beginnarrower
+  \nonproportional{\string\font\string\fontname\space = [}%
+  \meta{/path/to/file}%
+  \nonproportional{]}
+\endnarrower
+
+\noindent
+Inside the square brackets, every character except for a closing
+bracket is permitted, allowing for specifying paths to a font file.
+%
+Naturally, path-less file names are equally valid and processed the
+same way as an ordinary \inlinecode {file:} lookup.
+
+\beginnarrower
+  \nonproportional{\string\font\string\fontname\space= }%
+  \meta{font name}
+  \dots
+\endnarrower
+
+Unbracketed (or, for lack of a better word: \emphasis{anonymous})
+font requests resemble the conventional \TEX syntax.
+%
+However, they have a broader spectrum of possible interpretations:
+before anything else, \identifier{luaotfload} attempts to load a
+traditional \TEX Font Metric (\abbrev{tfm} or \abbrev{ofm}).
+%
+If this fails, it performs a \inlinecode {name:} lookup, which itself will
+fall back to a \inlinecode {file:} lookup if no database entry matches
+\meta{font name}.
+
+Furthermore, \identifier{luaotfload} supports the slashed (shorthand)
+font style notation from \XETEX.
+
+\beginnarrower
+  \nonproportional{\string\font\string\fontname\space= }%
+  \meta{font name}%
+  \nonproportional{/}%
+  \meta{modifier}
+  \dots
+\endnarrower
+
+\noindent
+Currently, four style modifiers are supported:
+  \inlinecode {I} for italic shape,
+  \inlinecode {B} for bold   weight,
+  \inlinecode {BI} or \inlinecode {IB} for the combination of both.
+%
+Other “slashed” modifiers are too specific to the \XETEX engine and
+have no meaning in \LUATEX.
+
+\endsubsection
+
+\beginsubsection{Examples}
+
+\beginsubsubsection{Loading by File Name}
+
+For example, conventional \abbrev{type1} font can be loaded with a
+\inlinecode {file:} request like so:
+
+\beginlisting
+  \font \lmromanten = {file:ec-lmr10} at 10pt
+\endlisting
+
+The \OpenType version of Janusz Nowacki’s font \emphasis{Antykwa
+Półtawskiego}\footnote{%
+  \hyperlink {http://jmn.pl/antykwa-poltawskiego/}, also available in
+  in \TEX Live.
+}
+in its condensed variant can be loaded as follows:
+
+\beginlisting
+  \font \apcregular = file:antpoltltcond-regular.otf at 42pt
+\endlisting
+
+The next example shows how to load the \emphasis{Porson} font digitized by
+the Greek Font Society using \XETEX-style syntax and an absolute path from a
+non-standard directory:
+
+\beginlisting
+  \font \gfsporson = "[/tmp/GFSPorson.otf]" at 12pt
+\endlisting
+
+\endsubsubsection
+
+\beginsubsubsection{Loading by Font Name}
+
+The \inlinecode {name:} lookup does not depend on cryptic filenames:
+
+\beginlisting
+  \font \pagellaregular = {name:TeX Gyre Pagella} at 9pt
+\endlisting
+
+A bit more specific but essentially the same lookup would be:
+
+\beginlisting
+  \font \pagellaregular = {name:TeX Gyre Pagella Regular} at 9pt
+\endlisting
+
+\noindent
+Which fits nicely with the whole set:
+
+\beginlisting
+  \font\pagellaregular    = {name:TeX Gyre Pagella Regular}    at 9pt
+  \font\pagellaitalic     = {name:TeX Gyre Pagella Italic}     at 9pt
+  \font\pagellabold       = {name:TeX Gyre Pagella Bold}       at 9pt
+  \font\pagellabolditalic = {name:TeX Gyre Pagella Bolditalic} at 9pt
+
+  {\pagellaregular     foo bar baz\endgraf}
+  {\pagellaitalic      foo bar baz\endgraf}
+  {\pagellabold        foo bar baz\endgraf}
+  {\pagellabolditalic  foo bar baz\endgraf}
+
+  ...
+\endlisting
+
+\endsubsubsection
+
+\beginsubsubsection{Modifiers}
+
+If the entire \emphasis{Iwona} family\footnote{%
+  \hyperlink {http://jmn.pl/kurier-i-iwona/},
+  also in \TEX Live.
+}
+is installed in some location accessible by \identifier{luaotfload},
+the regular shape can be loaded as follows:
+
+\beginlisting
+  \font \iwona = Iwona at 20pt
+\endlisting
+
+\noindent
+To load the most common of the other styles, the slash notation can
+be employed as shorthand:
+
+\beginlisting
+  \font \iwonaitalic     = Iwona/I    at 20pt
+  \font \iwonabold       = Iwona/B    at 20pt
+  \font \iwonabolditalic = Iwona/BI   at 20pt
+\endlisting
+
+\noindent
+which is equivalent to these full names:
+
+\beginlisting
+  \font \iwonaitalic     = "Iwona Italic"       at 20pt
+  \font \iwonabold       = "Iwona Bold"         at 20pt
+  \font \iwonabolditalic = "Iwona BoldItalic"   at 20pt
+\endlisting
+
+\endsubsubsection
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Font features}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\emphasis{Font features} are the second to last component in the
+general scheme for font requests:
+
+\beginnarrower
+  \nonproportional{\string\font\string\foo\space= "}%
+  \meta{prefix}%
+  \nonproportional{:}%
+  \meta{font name}%
+  \nonproportional{:}%
+  \meta{font features}%
+  \meta{\TEX font features}%
+  \nonproportional{"}
+\endnarrower
+
+\noindent
+If style modifiers are present (\XETEX style), they must precede
+\meta{font features}.
+
+The element \meta{font features} is a semicolon-separated list of feature
+tags\footnote{%
+  Cf. \hyperlink {http://www.microsoft.com/typography/otspec/featurelist.htm}.
+}
+and font options.
+%
+Prepending a font feature with a \inlinecode{+} (plus sign) enables it,
+whereas a \inlinecode{-} (minus) disables it. For instance, the request
+
+\beginlisting
+  \font \test = LatinModernRoman:+clig;-kern
+\endlisting
+
+\noindent activates contextual ligatures (\inlinecode{clig}) and
+disables kerning (\inlinecode{kern}).
+%
+Alternatively the options \inlinecode{true} or \inlinecode{false} can
+be passed to the feature in a key/value expression.
+%
+The following request has the same meaning as the last one:
+
+\beginlisting
+  \font \test = LatinModernRoman:clig=true;kern=false
+\endlisting
+
+\noindent
+Furthermore, this second syntax is required should a font feature
+accept other options besides a true/false switch.
+%
+For example, \emphasis{stylistic alternates} (\inlinecode{salt}) are
+variants of given glyphs.
+%
+They can be selected either explicitly by supplying the variant
+index (starting from one), or randomly by setting the value to,
+obviously, \inlinecode{random}.
+
+%% TODO   verify that this actually works with a font that supports
+%%        the salt/random feature!\fi
+\beginlisting
+  \font \librmsaltfirst = LatinModernRoman:salt=1
+\endlisting
+
+\beginsubsection {Basic font features}
+
+\begindescriptions
+
+  \beginaltitem {mode}
+         \identifier{luaotfload} has two \OpenType processing
+         \emphasis{modes}:
+         \identifier{base} and \identifier{node}.
+
+         \identifier{base} mode works by mapping \OpenType
+         features to traditional \TEX ligature and kerning mechanisms.
+         %
+         Supporting only non-contextual substitutions and kerning
+         pairs, it is the slightly faster, albeit somewhat limited, variant.
+         %
+         \identifier{node} mode works by processing \TeX’s internal
+         node list directly at the \LUA end and supports
+         a wider range of \OpenType features.
+         %
+         The downside is that the intricate operations required for
+         \identifier{node} mode may slow down typesetting especially
+         with complex fonts and it does not work in math mode.
+
+         By default \identifier{luaotfload} is in \identifier{node}
+         mode, and \identifier{base} mode has to be requested where needed,
+         e.~g. for math fonts.
+  \endaltitem
+
+  \beginaltitem {script} \label{script-tag}
+         An \OpenType script tag;\footnote{%
+           See \hyperlink {http://www.microsoft.com/typography/otspec/scripttags.htm}
+           for a list of valid values.
+           %
+           For scripts derived from the Latin alphabet the value
+           \inlinecode{latn} is good choice.
+         }
+         the default value is \inlinecode{dlft}.
+         %
+         Some fonts, including very popular ones by foundries like Adobe,
+         do not assign features to the \inlinecode{dflt} script, in
+         which case the script needs to be set explicitly.
+  \endaltitem
+
+  \beginaltitem {language}
+         An \OpenType language system identifier,\footnote{%
+           Cf. \hyperlink {http://www.microsoft.com/typography/otspec/languagetags.htm}.
+         }
+         defaulting to \inlinecode{dflt}.
+  \endaltitem
+
+  \beginaltitem {featurefile}
+         A comma-separated list of feature files to be applied to the
+         font.
+         %
+         Feature files contain a textual representation of
+         \OpenType tables and extend the features of a font
+         on fly.
+         %
+         After they are applied to a font, features defined in a
+         feature file can be enabled or disabled just like any
+         other font feature.
+         %
+         The syntax is documented in \identifier{Adobe}’s
+         \OpenType Feature File Specification.\footnote{%
+           Cf. \hyperlink {http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html}.
+           Feature file support is part of the engine which at the
+           time of this writing (2014) implements the spec only
+           partially.
+           See the
+           \hyperlink [\LUATEX tracker]{http://tracker.luatex.org/view.php?id=231}
+            for details.
+         }
+
+         For a demonstration of how to set a \inlinecode{tkrn} feature consult
+         the file \inlinecode{tkrn.fea} that is part of \identifier{luaotfload}.
+         It can be read and applied as follows:
+
+         \inlinecode{\\font \\test = Latin Modern Roman:featurefile=tkrn.fea;+tkrn}
+  \endaltitem
+
+  \beginaltitem {color}
+         A font color, defined as a triplet of two-digit hexadecimal
+         \abbrev{rgb} values, with an optional fourth value for
+         transparency
+         (where \inlinecode{00} is completely transparent and
+         \inlinecode{FF} is opaque).
+
+         For example, in order to set text in semitransparent red:
+
+         \beginlisting
+\font \test = "Latin Modern Roman:color=FF0000BB"
+         \endlisting
+  \endaltitem
+
+  \beginaltitem {kernfactor \& letterspace}
+         Define a font with letterspacing (tracking) enabled.
+         %
+         In \identifier{luaotfload}, letterspacing is implemented by
+         inserting additional kerning between glyphs.
+
+         This approach is derived from and still quite similar to the
+         \emphasis{character kerning} (\texmacro{setcharacterkerning} /
+         \texmacro{definecharacterkerning} \& al.) functionality of
+         Context, see the file \fileent{typo-krn.lua} there.
+         %
+         The main difference is that \identifier{luaotfload} does not
+         use \LUATEX attributes to assign letterspacing to regions,
+         but defines virtual letterspaced versions of a font.
+
+         The option \identifier{kernfactor} accepts a numeric value that
+         determines the letterspacing factor to be applied to the font
+         size.
+         %
+         E.~g. a kern factor of $0.42$ applied to a $10$ pt font
+         results in $4.2$ pt of additional kerning applied to each
+         pair of glyphs.
+         %
+         Ligatures are split into their component glyphs unless
+         explicitly ignored (see below).
+
+         For compatibility with \XETEX an alternative
+         \identifier{letterspace} option is supplied that interprets the
+         supplied value as a \emphasis{percentage} of the font size but
+         is otherwise identical to \identifier{kernfactor}.
+         %
+         Consequently, both definitions in below snippet yield the same
+         letterspacing width:
+
+         \beginlisting
+\font \iwonakernedA = "file:Iwona-Regular.otf:kernfactor=0.125"
+\font \iwonakernedB = "file:Iwona-Regular.otf:letterspace=12.5"
+         \endlisting
+
+         Specific pairs of letters and ligatures may be exempt from
+         letterspacing by defining the \LUA functions
+         \luafunction{keeptogether} and \luafunction{keepligature},
+         respectively, inside the namespace \inlinecode {luaotfload.letterspace}.
+         %
+         Both functions are called whenever the letterspacing callback
+         encounters an appropriate node or set of nodes.
+         %
+         If they return a true-ish value, no extra kern is inserted at
+         the current position.
+         %
+         \luafunction{keeptogether} receives a pair of consecutive
+         glyph nodes in order of their appearance in the node list.
+         %
+         \luafunction{keepligature} receives a single node which can be
+         analyzed into components.
+         %
+         (For details refer to the \emphasis{glyph nodes} section in the
+         \LUATEX reference manual.)
+         %
+         The implementation of both functions is left entirely to the
+         user.
+  \endaltitem
+
+\ifcontextmkiv
+  \startbuffer [printvectors]
+  \directlua{inspect(fonts.protrusions.setups.default)
+             inspect(fonts.expansions.setups.default)}
+  \stopbuffer
+\fi
+
+  \beginaltitem {protrusion \& expansion}
+         These keys control microtypographic features of the font,
+         namely \emphasis{character protrusion} and \emphasis{font
+         expansion}.
+         %
+         Their arguments are names of \LUA tables that contain
+         values for the respective features.\footnote{%
+            For examples of the table layout please refer to the
+            section of the file \fileent{luaotfload-fonts-ext.lua} where the
+            default values are defined.
+            %
+            Alternatively and with loss of information, you can dump
+            those tables into your terminal by issuing
+            \unless \ifcontextmkiv
+              \beginlisting
+ \directlua{inspect(fonts.protrusions.setups.default)
+            inspect(fonts.expansions.setups.default)}
+              \endlisting
+            \else
+              \typebuffer [printvectors]
+            \fi
+            at some point after loading \fileent{luaotfload.sty}.
+         }
+         %
+         For both, only the set \identifier{default} is predefined.
+
+         For example, to define a font with the default
+         protrusion vector applied\footnote{%
+           You also need to set
+               \inlinecode {pdfprotrudechars=2} and
+               \inlinecode {pdfadjustspacing=2}
+           to activate protrusion and expansion, respectively.
+           See the
+           \hyperlink [\PDFTEX manual]{http://mirrors.ctan.org/systems/pdftex/manual/pdftex-a.pdf}%
+           for details.
+         }:
+
+         \beginlisting
+\font \test = LatinModernRoman:protrusion=default
+         \endlisting
+  \endaltitem
+\enddescriptions
+
+\endsubsection
+
+\beginsubsection {Non-standard font features}
+\identifier{luaotfload} adds a number of features that are not defined
+in the original \OpenType specification, most of them
+aiming at emulating the behavior familiar from other \TEX engines.
+%
+Currently (2014) there are three of them:
+
+\begindescriptions
+
+  \beginaltitem {anum}
+          Substitutes the glyphs in the \abbrev{ascii} number range
+          with their counterparts from eastern Arabic or Persian,
+          depending on the value of \identifier{language}.
+  \endaltitem
+
+  \beginaltitem {tlig}
+          Applies legacy \TEX ligatures\footnote{%
+            These contain the feature set \inlinecode {trep} of earlier
+            versions of \identifier{luaotfload}.
+
+            Note to \XETEX users: this is the equivalent of the
+            assignment \inlinecode {mapping=text-tex} using \XETEX's input
+            remapping feature.
+          }:
+
+          \unless \ifcontextmkiv
+            %% Using braced arg syntax with inline code appears to be
+            %% impossible within Latex tables -- just ignore the weird
+            %% exclamation points below.
+            \begintabulate [rlrl]
+              \beginrow ``  \newcell  {\inlinecode !``! } \newcell  ''  \newcell  {\inlinecode !''!} \endrow
+              \beginrow `   \newcell  {\inlinecode !`!  } \newcell  '   \newcell  {\inlinecode !'! } \endrow
+              \beginrow "   \newcell  {\inlinecode !"!  } \newcell  --  \newcell  {\inlinecode !--!} \endrow
+              \beginrow --- \newcell  {\inlinecode !---!} \newcell  !`  \newcell  {\inlinecode ?!`?} \endrow
+              \beginrow ?`  \newcell  {\inlinecode !?`! } \newcell      \newcell                     \endrow
+            \endtabulate
+          \else
+            %% XXX find a way to wrap these in the tabulate environment
+            \startframed [frame=off,width=broad,align=middle]
+              \startframed [frame=off,width=\dimexpr(\textwidth/2)]
+                \startxtable [align=middle]
+                    \startxrow \startxcell ``  \stopxcell \startxcell  \inlinecode {``}  \stopxcell \startxcell  ''  \stopxcell \startxcell  \inlinecode {''}  \stopxcell \stopxrow
+                    \startxrow \startxcell `   \stopxcell \startxcell  \inlinecode {`}   \stopxcell \startxcell  '   \stopxcell \startxcell  \inlinecode {'}   \stopxcell \stopxrow
+                    \startxrow \startxcell "   \stopxcell \startxcell  \inlinecode {"}   \stopxcell \startxcell  --  \stopxcell \startxcell  \inlinecode {--}  \stopxcell \stopxrow
+                    \startxrow \startxcell --- \stopxcell \startxcell  \inlinecode {---} \stopxcell \startxcell  !`  \stopxcell \startxcell  \inlinecode {!`}  \stopxcell \stopxrow
+                    \startxrow \startxcell ?`  \stopxcell \startxcell  \inlinecode {?`}  \stopxcell \startxcell      \stopxcell \startxcell                    \stopxcell \stopxrow
+                \stopxtable
+              \stopframed
+            \stopframed
+          \fi
+  \endaltitem
+
+  \beginaltitem {itlc}
+          Computes italic correction values (active by default).
+  \endaltitem
+
+\enddescriptions
+
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Font names database}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\label{sec:fontdb}
+
+As mentioned above, \identifier{luaotfload} keeps track of which
+fonts are available to \LUATEX by means of a \emphasis{database}.
+%
+This allows referring to fonts not only by explicit filenames but
+also by the proper names contained in the metadata which is often
+more accessible to humans.\footnote{%
+  The tool \hyperlink[\fileent{otfinfo}]{http://www.lcdf.org/type/}
+  (comes with \TEX Live), when invoked on a font file with the
+  \inlinecode {-i} option, lists the variety of name fields defined for
+  it.
+}
+
+When \identifier{luaotfload} is asked to load a font by a font name,
+it will check if the database exists and load it, or else generate a
+fresh one.
+%
+Should it then fail to locate the font, an update to the database is
+performed in case the font has been added to the system only
+recently.
+%
+As soon as the database is updated, the resolver will try
+and look up the font again, all without user intervention.
+%
+The goal is for \identifier{luaotfload} to act in the background and
+behave as unobtrusively as possible, while providing a convenient
+interface to the fonts installed on the system.
+
+Generating the database for the first time may take a while since it
+inspects every font file on your computer.
+%
+This is particularly noticeable if it occurs during a typesetting run.
+In any case, subsequent updates to the database will be quite fast.
+
+\beginsubsection[luaotfload-tool]
+                {\fileent{luaotfload-tool}}
+
+It can still be desirable at times to do some of these steps
+manually, and without having to compile a document.
+%
+To this end, \identifier{luaotfload} comes with the utility
+\fileent{luaotfload-tool} that offers an interface to the database
+functionality.
+%
+Being a \LUA script, there are two ways to run it:
+either make it executable (\inlinecode {chmod +x} on unixoid systems) or
+pass it as an argument to \fileent{texlua}.\footnote{%
+  Tests by the maintainer show only marginal performance gain by
+  running with Luigi Scarso’s
+  \hyperlink [\identifier{Luajit\kern-.25ex\TEX}]{https://foundry.supelec.fr/projects/luajittex/},
+  which is probably due to the fact that most of the time is spent
+  on file system operations.
+
+  \emphasis{Note}:
+  On \abbrev{MS} \identifier{Windows} systems, the script can be run
+  either by calling the wrapper application
+  \fileent{luaotfload-tool.exe} or as
+  \inlinecode {texlua.exe luaotfload-tool.lua}.
+}
+%
+Invoked with the argument \inlinecode {--update} it will perform a database
+update, scanning for fonts not indexed.
+
+\beginlisting
+  luaotfload-tool --update
+\endlisting
+
+Adding the \inlinecode {--force} switch will initiate a complete
+rebuild of the database.
+
+\beginlisting
+  luaotfload-tool --update --force
+\endlisting
+
+\endsubsection
+
+\beginsubsection{Search Paths}
+
+\identifier{luaotfload} scans those directories where fonts are
+expected to be located on a given system.
+%
+On a Linux machine it follows the paths listed in the
+\identifier{Fontconfig} configuration files;
+consult \inlinecode {man 5 fonts.conf} for further information.
+%
+On \identifier{Windows} systems, the standard location is
+\inlinecode {Windows\\Fonts},
+%
+while \identifier{Mac OS~X} requires a multitude of paths to
+be examined.
+%
+The complete list is is given in table \ref{table-searchpaths}.
+Other paths can be specified by setting the environment variable
+\inlinecode {OSFONTDIR}.
+%
+If it is non-empty, then search will be extended to the included
+directories.
+
+\tablefloat {table-searchpaths}
+  {List of paths searched for each supported operating system.}
+  {%
+    \unless \ifcontextmkiv
+      \begincentered
+        \begintabulate [lp{.5\textwidth}]
+          \beginrow
+            Windows   \newcell \inlinecode !\% WINDIR\%\\ Fonts!
+          \endrow
+          \beginrow
+            Linux     \newcell \fileent{/usr/local/etc/fonts/fonts.conf} and\hfill\break
+                               \fileent{/etc/fonts/fonts.conf}
+          \endrow
+          \beginrow
+            Mac       \newcell \fileent{\textasciitilde/Library/Fonts},\break
+                               \fileent{/Library/Fonts},\break
+                               \fileent{/System/Library/Fonts}, and\hfill\break
+                               \fileent{/Network/Library/Fonts}
+          \endrow
+        \endtabulate
+      \endcentered
+    \else
+      \setuplocalinterlinespace [14pt]
+      \starttabulate [|l|p(.5\textwidth)|]
+        \NC Windows   \NC \inlinecode {\% WINDIR\%\\ Fonts} \NC \NR
+        \NC Linux     \NC \fileent{/usr/local/etc/fonts/fonts.conf} and\crlf
+                          \fileent{/etc/fonts/fonts.conf} \NC \NR
+        \NC
+          Mac         \NC \fileent{\textasciitilde/Library/Fonts},\crlf
+                          \fileent{/Library/Fonts},\break
+                          \fileent{/System/Library/Fonts}, and\crlf
+                          \fileent{/Network/Library/Fonts} \NC \NR
+      \stoptabulate
+    \fi%
+  }
+
+\endsubsection
+
+\beginsubsection{Querying from Outside}
+
+\fileent{luaotfload-tool} also provides rudimentary means of
+accessing the information collected in the font database.
+%
+If the option \inlinecode {--find=}\emphasis{name} is given, the script will
+try and search the fonts indexed by \identifier{luaotfload} for a
+matching name.
+%
+For instance, the invocation
+
+\beginlisting
+  luaotfload-tool  --find="Iwona Regular"
+\endlisting
+
+\noindent
+will verify if “Iwona Regular” is found in the database and can be
+readily requested in a document.
+
+If you are unsure about the actual font name, then add the
+\inlinecode {-F} (or \inlinecode {--fuzzy}) switch to the command line to enable
+approximate matching.
+%
+Suppose you cannot precisely remember if the variant of
+\identifier{Iwona} you are looking for was “Bright” or “Light”.
+The query
+
+\beginlisting
+  luaotfload-tool  -F --find="Iwona Bright"
+\endlisting
+
+\noindent
+will tell you that indeed the latter name is correct.
+
+Basic information about fonts in the database can be displayed
+using the \inlinecode {-i} option (\inlinecode {--info}).
+%
+\beginlisting
+  luaotfload-tool  -i --find="Iwona Light Italic"
+\endlisting
+%
+\noindent
+The meaning of the printed values is described in section 4.4 of the
+\LUATEX reference manual.\footnote{%
+  In \TEX Live: \fileent{texmf-dist/doc/luatex/base/luatexref-t.pdf}.
+}
+
+For a much more detailed report about a given font try the
+\inlinecode {-I} option instead (\inlinecode {--inspect}).
+\beginlisting
+  luaotfload-tool  -I --find="Iwona Light Italic"
+\endlisting
+
+\inlinecode {luaotfload-tool --help} will list the available command line
+switches, including some not discussed in detail here.
+%
+For a full documentation of \identifier{luaotfload-tool} and its
+capabilities refer to the manpage
+(\inlinecode {man 1 luaotfload-tool}).\footnote{%
+  Or see \inlinecode {luaotfload-tool.rst} in the source directory.
+}
+
+\endsubsection
+
+\beginsubsection {Blacklisting Fonts}
+\label{font-blacklist}
+
+Some fonts are problematic in general, or just in \LUATEX.
+%
+If you find that compiling your document takes far too long or eats
+away all your system’s memory, you can track down the culprit by
+running \inlinecode {luaotfload-tool -v} to increase verbosity.
+%
+Take a note of the \emphasis{filename} of the font that database
+creation fails with and append it to the file
+\fileent{luaotfload-blacklist.cnf}.
+
+A blacklist file is a list of font filenames, one per line.
+Specifying the full path to where the file is located is optional, the
+plain filename should suffice.
+%
+File extensions (\fileent{.otf}, \fileent{.ttf}, etc.) may be omitted.
+%
+Anything after a percent (\inlinecode {\%}) character until the end of the line
+is ignored, so use this to add comments.
+%
+Place this file to some location where the \identifier{kpse}
+library can find it, e.~g.
+\fileent{texmf-local/tex/luatex/luaotfload} if you are running
+\identifier{\TEX Live},\footnote{%
+  You may have to run \inlinecode {mktexlsr} if you created a new file in
+  your \fileent{texmf} tree.
+}
+or just leave it in the working directory of your document.
+%
+\identifier{luaotfload} reads all files named
+\fileent{luaotfload-blacklist.cnf} it finds, so the fonts in
+\fileent{./luaotfload-blacklist.cnf} extend the global blacklist.
+
+Furthermore, a filename prepended with a dash character (\inlinecode{-}) is
+removed from the blacklist, causing it to be temporarily whitelisted
+without modifying the global file.
+%
+An example with explicit paths:
+
+\beginlisting
+% example otf-blacklist.cnf
+/Library/Fonts/GillSans.ttc  % Luaotfload ignores this font.
+-/Library/Fonts/Optima.ttc   % This one is usable again, even if
+                             % blacklisted somewhere else.
+\endlisting
+
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Files from \CONTEXT and \LUATEX-Fonts}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\identifier{luaotfload} relies on code originally written by Hans
+Hagen for the \hyperlink[\identifier{\CONTEXT}]{http://wiki.contextgarden.net}
+format.
+%
+It integrates the font loader as distributed in
+the \identifier{\LUATEX-Fonts} package.
+%
+The original \LUA source files have been combined using the
+\fileent{mtx-package} script into a single, self-contained blob.
+In this form the font loader has no further dependencies\footnote{%
+  It covers, however, to some extent the functionality of the
+  \identifier{lualibs} package.
+}
+and requires only minor adaptions to integrate into
+\identifier{luaotfload}.
+%
+The guiding principle is to let \CONTEXT/\LUATEX-Fonts take care of
+the implementation, and update the imported code from time to time.
+%
+As maintainers, we aim at importing files from upstream essentially
+\emphasis{unmodified}, except for renaming them to prevent name
+clashes.
+%
+This job has been greatly alleviated since the advent of
+\LUATEX-Fonts, prior to which the individual dependencies had to be
+manually spotted and extracted from the \CONTEXT source code in a
+complicated and error-prone fashion.
+
+Below is a commented list of the files distributed with
+\identifier{luaotfload} in one way or the other.
+%
+See figure \ref{file-graph} on page \pageref{file-graph} for a
+graphical representation of the dependencies.
+%
+From \LUATEX-Fonts, only the file \fileent{luatex-fonts-merged.lua}
+has been imported as \fileent{luaotfload-fontloader.lua}.
+%
+It is generated by \fileent{mtx-package}, a \LUA source code merging
+too developed by Hans Hagen.\footnote{%
+  \fileent{mtx-package} is
+  \hyperlink [part of \CONTEXT]{http://repo.or.cz/w/context.git/blob_plain/refs/heads/origin:/scripts/context/lua/mtx-package.lua}
+  and requires \fileent{mtxrun}.
+  Run
+  \inlinecode {mtxrun --script package --help}
+  to display further information.
+  For the actual merging code see the file
+  \fileent{util-mrg.lua} that is part of \CONTEXT.
+}
+It houses several \LUA files that can be classed in three
+categories.
+
+\begindefinitions
+  \beginnormalitem
+    \emphasis{\LUA utility libraries}, a subset
+    of what is provided by the \identifier{lualibs}
+    package.
+
+    \begindoublecolumns
+      \begindefinitions
+          \beginaltitem {l-lua.lua}       \endaltitem
+          \beginaltitem {l-lpeg.lua}      \endaltitem
+          \beginaltitem {l-function.lua}  \endaltitem
+          \beginaltitem {l-string.lua}    \endaltitem
+          \beginaltitem {l-table.lua}     \endaltitem
+          \beginaltitem {l-io.lua}        \endaltitem
+          \beginaltitem {l-file.lua}      \endaltitem
+          \beginaltitem {l-boolean.lua}   \endaltitem
+          \beginaltitem {l-math.lua}      \endaltitem
+          \beginaltitem {util-str.lua}    \endaltitem
+      \enddefinitions
+    \enddoublecolumns
+  \endnormalitem
+
+  \beginnormalitem
+    The \emphasis{font loader} itself.
+    These files have been written for
+    \LUATEX-Fonts and they are distributed along
+    with \identifier{luaotfload}.
+    \begindoublecolumns
+      \begindefinitions
+        \beginaltitem{luatex-basics-gen.lua} \endaltitem
+        \beginaltitem{luatex-basics-nod.lua} \endaltitem
+        \beginaltitem{luatex-fonts-enc.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-syn.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-tfm.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-chr.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-lua.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-inj.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-otn.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-def.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-ext.lua}  \endaltitem
+        \beginaltitem{luatex-fonts-cbk.lua}  \endaltitem
+      \enddefinitions
+    \enddoublecolumns
+  \endnormalitem
+
+  \beginnormalitem
+    Code related to \emphasis{font handling and
+    node processing}, taken directly from
+    \CONTEXT.
+    \begindoublecolumns
+      \begindefinitions
+        \beginaltitem{data-con.lua} \endaltitem
+        \beginaltitem{font-ini.lua} \endaltitem
+        \beginaltitem{font-con.lua} \endaltitem
+        \beginaltitem{font-cid.lua} \endaltitem
+        \beginaltitem{font-map.lua} \endaltitem
+        \beginaltitem{font-oti.lua} \endaltitem
+        \beginaltitem{font-otf.lua} \endaltitem
+        \beginaltitem{font-otb.lua} \endaltitem
+        \beginaltitem{font-ota.lua} \endaltitem
+        \beginaltitem{font-def.lua} \endaltitem
+        \beginaltitem{font-otp.lua} \endaltitem
+      \enddefinitions
+    \enddoublecolumns
+  \endnormalitem
+\enddefinitions
+
+Note that if \identifier{luaotfload} cannot locate the
+merged file, it will load the individual \LUA libraries
+instead.
+%
+Their names remain the same as in \CONTEXT (without the
+\inlinecode {otfl}-prefix) since we imported the relevant section of
+\fileent{luatex-fonts.lua} unmodified into \fileent{luaotfload-main.lua}.
+Thus if you prefer running bleeding edge code from the
+\CONTEXT beta, all you have to do is remove
+\fileent{luaotfload-merged.lua} from the search path.
+
+Also, the merged file at some point loads the Adobe Glyph List from a
+\LUA table that is contained in \fileent{luaotfload-glyphlist.lua},
+which is automatically generated by the script
+\fileent{mkglyphlist}.\footnote{%
+  See \fileent{luaotfload-font-enc.lua}.
+  The hard-coded file name is why we have to replace the procedure
+  that loads the file in \fileent{luaotfload-override.lua}.
+}
+There is a make target \identifier{glyphs} that will create a fresh
+glyph list so we don’t need to import it from \CONTEXT any longer.
+
+In addition to these, \identifier{luaotfload} requires a number of
+files not contained in the merge. Some of these have no equivalent in
+\LUATEX-Fonts or \CONTEXT, some were taken unmodified from the latter.
+
+
+\beginfilelist
+    \beginaltitem {luaotfload-features.lua}
+      font feature handling; incorporates some of the code from
+      \fileent{font-otc} from \CONTEXT;
+    \endaltitem
+    \beginaltitem {luaotfload-override.lua}
+      overrides the \CONTEXT logging functionality.
+    \endaltitem
+    \beginaltitem {luaotfload-loaders.lua}
+      registers the \OpenType font reader as handler for Postscript
+      fonts (\abbrev{pfa}, \abbrev{pfb}).
+    \endaltitem
+    \beginaltitem {luaotfload-parsers.lua}
+      various \abbrev{lpeg}-based parsers.
+    \endaltitem
+    \beginaltitem {luaotfload-database.lua}
+      font names database.
+    \endaltitem
+    \beginaltitem {luaotfload-colors.lua}
+      color handling.
+    \endaltitem
+    \beginaltitem {luaotfload-auxiliary.lua}
+      access to internal functionality for package authors (proposals
+      for additions welcome).
+    \endaltitem
+    \beginaltitem {luaotfload-letterspace.lua}
+      font-based letterspacing.
+    \endaltitem
+\endfilelist
+
+\figurefloat
+  {file-graph}
+  {Schematic of the files in \identifier{Luaotfload}}
+  {filegraph.pdf}
+
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Auxiliary Functions}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+With release version 2.2, \identifier{luaotfload} received
+additional functions for package authors to call from outside
+(see the file \fileent{luaotfload-auxiliary.lua} for details).
+%
+The purpose of this addition twofold.
+%
+Firstly, \identifier{luaotfload} failed to provide a stable interface
+to internals in the past which resulted in an unmanageable situation
+of different packages abusing the raw access to font objects by means
+of the \luafunction{patch_font} callback.
+%
+When the structure of the font object changed due to an update, all
+of these imploded and several packages had to be fixed while
+simultaneously providing fallbacks for earlier versions.
+%
+Now the patching is done on the \identifier{luaotfload} side and can
+be adapted with future modifications to font objects without touching
+the packages that depend on it.
+%
+Second, some the capabilities of the font loader and the names
+database are not immediately relevant in \identifier{luaotfload}
+itself but might nevertheless be of great value to package authors or
+end users.
+
+Note that the current interface is not yet set in stone and the
+development team is open to suggestions for improvements or
+additions.
+
+\beginsubsection {Callback Functions}
+
+The \luafunction{patch_font} callback is inserted in the wrapper
+\identifier{luaotfload} provides for the font definition callback
+(see below, page \pageref{define-font}).
+%
+At this place it allows manipulating the font object immediately after
+the font loader is done creating it.
+%
+For a short demonstration of its usefulness, here is a snippet that
+writes an entire font object to the file \fileent{fontdump.lua}:
+
+\beginlisting
+  \input luaotfload.sty
+  \directlua{
+    local dumpfile    = "fontdump.lua"
+    local dump_font   = function (tfmdata)
+      local data = table.serialize(tfmdata)
+      io.savedata(dumpfile, data)
+    end
+
+    luatexbase.add_to_callback(
+      "luaotfload.patch_font",
+      dump_font,
+      "my_private_callbacks.dump_font"
+    )
+  }
+  \font \dumpme = name:Iwona
+  \bye
+\endlisting
+
+\emphasis{Beware}: this creates a Lua file of around 150,000 lines of
+code, taking up 3~\abbrev{mb} of disk space.
+%
+By inspecting the output you can get a first impression of how a font
+is structured in \LUATEX’s memory, what elements it is composed of,
+and in what ways it can be rearranged.
+
+\beginsubsubsection {Compatibility with Earlier Versions}
+
+As has been touched on in the preface to this section, the structure
+of the object as returned by the fontloader underwent rather drastic
+changes during different stages of its development, and not all
+packages that made use of font patching have kept up with every one
+of it.
+%
+To ensure compatibility with these as well as older versions of
+some packages, \identifier{luaotfload} sets up copies of or references
+to data in the font table where it used to be located.
+%
+For instance, important parameters like the requested point size, the
+units factor, and the font name have again been made accessible from
+the toplevel of the table even though they were migrated to different
+subtables in the meantime.
+
+\endsubsubsection
+
+\beginsubsubsection{Patches}
+
+These are mostly concerned with establishing compatibility with \XETEX.
+
+\beginfunctionlist
+
+  \beginaltitem  {set_sscale_dimens}
+    Calculate \texmacro{fontdimen}s 10 and 11 to emulate \XETEX.
+  \endaltitem
+
+  \beginaltitem  {set_capheight}
+    Calculates \texmacro{fontdimen} 8 like \XETEX.
+  \endaltitem
+
+  \beginaltitem  {patch_cambria_domh}
+    Correct some values of the font \emphasis{Cambria Math}.
+  \endaltitem
+
+\endfunctionlist
+
+\endsubsection
+
+\beginsubsection {Package Author’s Interface}
+
+As \LUATEX release 1.0 is nearing, the demand for a reliable interface
+for package authors increases.
+
+\endsubsubsection
+
+\beginsubsubsection{Font Properties}
+
+Below functions mostly concern querying the different components of a
+font like for instance the glyphs it contains, or what font features
+are defined for which scripts.
+
+\beginfunctionlist
+
+  \beginaltitem  {aux.font_has_glyph (id : int, index : int)}
+            Predicate that returns true if the font \luafunction{id}
+            has glyph \luafunction{index}.
+  \endaltitem
+
+  \beginaltitem  {aux.slot_of_name(name : string)}
+            Translates an Adobe Glyph name to the corresponding glyph
+            slot.
+  \endaltitem
+
+  \beginaltitem  {aux.name_of_slot(slot : int)}
+            The inverse of \luafunction{slot_of_name}; note that this
+            might be incomplete as multiple glyph names may map to the
+            same codepoint, only one of which is returned by
+            \luafunction{name_of_slot}.
+  \endaltitem
+
+  \beginaltitem  {aux.provides_script(id : int, script : string)}
+            Test if a font supports \luafunction{script}.
+  \endaltitem
+
+  \beginaltitem  {aux.provides_language(id : int, script : string, language : string)}
+            Test if a font defines \luafunction{language} for a given
+            \luafunction{script}.
+  \endaltitem
+
+  \beginaltitem  {aux.provides_feature(id : int, script : string,
+             language : string, feature : string)}
+            Test if a font defines \luafunction{feature} for
+            \luafunction{language} for a given \luafunction{script}.
+  \endaltitem
+
+  \beginaltitem  {aux.get_math_dimension(id : int, dimension : string)}
+            Get the dimension \luafunction{dimension} of font \luafunction{id}.
+  \endaltitem
+
+  \beginaltitem  {aux.sprint_math_dimension(id : int, dimension : string)}
+            Same as \luafunction{get_math_dimension()}, but output the value
+            in scaled points at the \TEX end.
+  \endaltitem
+
+\endfunctionlist
+
+\endsubsubsection
+
+\beginsubsubsection{Database}
+
+%% not implemented, may come back later
+\beginfunctionlist
+%   \beginaltitem  {aux.scan_external_dir(dir : string)}
+%             Include fonts in directory \luafunction{dir} in font lookups without
+%             adding them to the database.
+%
+  \beginaltitem  {aux.read_font_index (void)}
+            Read the index file from the appropriate location (usually
+            the bytecode file \fileent{luaotfload-names.luc} somewhere
+            in the \fileent{texmf-var} tree) and return the result as a
+            table. The file is processed with each call so it is up to
+            the user to store the result for later access.
+  \endaltitem
+
+  \beginaltitem  {aux.font_index (void)}
+            Return a reference of the font names table used internally
+            by \identifier{luaotfload}. The index will be read if it
+            has not been loaded up to this point. Also a font scan that
+            overwrites the current index file might be triggered. Since
+            the return value points to the actual index, any
+            modifications to the table might influence runtime behavior
+            of \identifier{luaotfload}.
+  \endaltitem
+
+\endfunctionlist
+
+\endsubsubsection
+
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Troubleshooting}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\beginsubsection {Database Generation}
+
+If you encounter problems with some fonts, please first update to the
+latest version of this package before reporting a bug, as
+\identifier{luaotfload} is under active development and still a moving
+target.
+%
+The development takes place on \identifier{github} at
+\hyperlink {https://github.com/lualatex/luaotfload} where there is an issue
+tracker for submitting bug reports, feature requests and the likes.
+
+Bug reports are more likely to be addressed if they contain the output
+of
+
+\beginlisting
+    luaotfload-tool --diagnose=environment,files,permissions
+\endlisting
+
+\noindent Consult the man page for a description of these options.
+
+Errors during database generation can be traced by increasing the
+verbosity level and redirecting log output to \fileent{stdout}:
+
+\beginlisting
+    luaotfload-tool -fuvvv --log=stdout
+\endlisting
+
+\noindent or to a file in \fileent{/tmp}:
+
+\beginlisting
+    luaotfload-tool -fuvvv --log=file
+\endlisting
+
+\noindent In the latter case, invoke the \inlinecode {tail(1)} utility on the
+file for live monitoring of the progress.
+
+If database generation fails, the font last printed to the terminal or
+log file is likely to be the culprit.
+%
+Please specify it when reporting a bug, and blacklist it for the time
+being (see above, page \pageref{font-blacklist}).
+
+\endsubsection
+
+\beginsubsection {Font Features}
+
+A common problem is the lack of features for some
+\OpenType fonts even when specified.
+%
+This can be related to the fact that some fonts do not provide features
+for the \inlinecode {dflt} script (see above on page \pageref{script-tag}),
+which is the default one in this package.
+%
+If this happens, assigning a noth script when the font is defined should
+fix it.
+%
+For example with \inlinecode {latn}:
+
+\beginlisting
+    \font \test = file:MyFont.otf:script=latn;+liga;
+\endlisting
+
+You can get a list of features that a font defines for scripts and
+languages by querying it in \fileent{luaotfload-tool}:
+
+\beginlisting
+    luaotfload-tool --find="Iwona" --inspect
+\endlisting
+
+\endsubsection
+
+\beginsubsection {\LUATEX Programming}
+
+Another strategy that helps avoiding problems is to not access raw
+\LUATEX internals directly.
+%
+Some of them, even though they are dangerous to access, have not been
+overridden or disabled.
+%
+Thus, whenever possible prefer the functions in the \luafunction{aux}
+namespace over direct manipulation of font objects. For example, raw
+access to the \luafunction{font.fonts} table like:
+
+\beginlisting
+    local somefont = font.fonts[2]
+\endlisting
+
+\noindent can render already defined fonts unusable.
+%
+Instead, the function \luafunction{font.getfont()} should be used
+because it has been replaced by a safe variant.
+
+However, \luafunction{font.getfont()} only covers fonts handled by the
+font loader, e.~g. \identifier{OpenType} and \identifier{TrueType}
+fonts, but not \abbrev{tfm} or \abbrev{ofm}.
+%
+Should you absolutely require access to all fonts known to \LUATEX,
+including the virtual and autogenerated ones, then you need to query
+both \luafunction{font.getfont()} and \luafunction{font.fonts}.
+%
+In this case, best define you own accessor:
+
+\beginlisting
+    local unsafe_getfont = function (id)
+        local tfmdata = font.getfont (id)
+        if not tfmdata then
+            tfmdata = font.fonts[id]
+        end
+        return tfmdata
+    end
+
+    --- use like getfont()
+    local somefont = unsafe_getfont (2)
+\endlisting
+
+\endsubsection
+\endsection
+
+\beginsection {License}
+
+\identifier {luaotfload} is licensed under the terms of the
+\hyperlink [GNU General Public License version 2.0]%
+           {https://www.gnu.org/licenses/old-licenses/gpl-2.0.html}.
+Following the underlying fontloader code \identifier {luaotfload}
+recognizes only that exact version as its license.
+The „any later version” clause of the original license text as
+copyrighted by the \hyperlink [Free Software Foundation]{http://www.fsf.org/}
+\emphasis {does not apply} to either \identifier {luaotfload} or the
+code imported from \CONTEXT.
+
+The complete text of the license is given as a separate file \fileent
+{COPYING} in the toplevel directory of the
+\hyperlink [\fileent {Luaotfload} Git repository]{https://github.com/lualatex/luaotfload/blob/master/COPYING}.
+Distributions probably package it as \fileent
+{doc/luatex/luaotfload/COPYING} in the relevant \fileent {texmf} tree.
+
+\endsection
+
+\endinput
+