xref: /xsrc/external/mit/fontconfig/dist/doc/fontconfig-user.sgml

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<refentry>
<refmeta>
  <refentrytitle>fonts-conf</refentrytitle>
  <manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
	<refname>fonts.conf</refname>
	<refpurpose>Font configuration files</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>
   &confdir;/fonts.conf
   &confdir;/fonts.dtd
   &confdir;/conf.d
   $XDG_CONFIG_HOME/fontconfig/conf.d
   $XDG_CONFIG_HOME/fontconfig/fonts.conf
   ~/.fonts.conf.d
   ~/.fonts.conf
</synopsis>
</refsynopsisdiv>
<refsect1><title>Description</title>
  <para>
Fontconfig is a library designed to provide system-wide font configuration,
customization and application access.
  </para>
</refsect1>
<refsect1><title>Functional Overview</title>
  <para>
Fontconfig contains two essential modules, the configuration module which
builds an internal configuration from XML files and the matching module
which accepts font patterns and returns the nearest matching font.
  </para>
  <refsect2><title>Font Configuration</title>
    <para>
The configuration module consists of the FcConfig datatype, libexpat and
FcConfigParse which walks over an XML tree and amends a configuration with
data found within.  From an external perspective, configuration of the
library consists of generating a valid XML tree and feeding that to
FcConfigParse.  The only other mechanism provided to applications for
changing the running configuration is to add fonts and directories to the
list of application-provided font files.  
    </para><para>
The intent is to make font configurations relatively static, and shared by
as many applications as possible.  It is hoped that this will lead to more
stable font selection when passing names from one application to another.
XML was chosen as a configuration file format because it provides a format
which is easy for external agents to edit while retaining the correct
structure and syntax.
    </para><para>
Font configuration is separate from font matching; applications needing to
do their own matching can access the available fonts from the library and
perform private matching.  The intent is to permit applications to pick and
choose appropriate functionality from the library instead of forcing them to
choose between this library and a private configuration mechanism.  The hope
is that this will ensure that configuration of fonts for all applications
can be centralized in one place.  Centralizing font configuration will
simplify and regularize font installation and customization.
    </para>
  </refsect2>
  <refsect2>
    <title>Font Properties</title>
    <para>
While font patterns may contain essentially any properties, there are some
well known properties with associated types.  Fontconfig uses some of these
properties for font matching and font completion.  Others are provided as a
convenience for the applications' rendering mechanism.
    </para>
    <programlisting>
  Property        Type    Description
  --------------------------------------------------------------
  family          String  Font family names
  familylang      String  Languages corresponding to each family
  style           String  Font style. Overrides weight and slant
  stylelang       String  Languages corresponding to each style
  fullname        String  Font full names (often includes style)
  fullnamelang    String  Languages corresponding to each fullname
  slant           Int     Italic, oblique or roman
  weight          Int     Light, medium, demibold, bold or black
  size            Double  Point size
  width           Int     Condensed, normal or expanded
  aspect          Double  Stretches glyphs horizontally before hinting
  pixelsize       Double  Pixel size
  spacing         Int     Proportional, dual-width, monospace or charcell
  foundry         String  Font foundry name
  antialias       Bool    Whether glyphs can be antialiased
  hinting         Bool    Whether the rasterizer should use hinting
  hintstyle       Int     Automatic hinting style
  verticallayout  Bool    Use vertical layout
  autohint        Bool    Use autohinter instead of normal hinter
  globaladvance   Bool    Use font global advance data (deprecated)
  file            String  The filename holding the font
  index           Int     The index of the font within the file
  ftface          FT_Face Use the specified FreeType face object
  rasterizer      String  Which rasterizer is in use (deprecated)
  outline         Bool    Whether the glyphs are outlines
  scalable        Bool    Whether glyphs can be scaled
  color           Bool    Whether any glyphs have color
  scale           Double  Scale factor for point->pixel conversions (deprecated)
  dpi             Double  Target dots per inch
  rgba            Int     unknown, rgb, bgr, vrgb, vbgr,
                          none - subpixel geometry
  lcdfilter       Int     Type of LCD filter
  minspace        Bool    Eliminate leading from line spacing
  charset         CharSet Unicode chars encoded by the font
  lang            String  List of RFC-3066-style languages this
                          font supports
  fontversion     Int     Version number of the font
  capability      String  List of layout capabilities in the font
  fontformat      String  String name of the font format
  embolden        Bool    Rasterizer should synthetically embolden the font
  embeddedbitmap  Bool    Use the embedded bitmap instead of the outline
  decorative      Bool    Whether the style is a decorative variant
  fontfeatures    String  List of the feature tags in OpenType to be enabled
  namelang        String  Language name to be used for the default value of
                          familylang, stylelang, and fullnamelang
  prgname         String  String  Name of the running program
  postscriptname  String  Font family name in PostScript
  fonthashint     Bool    Whether the font has hinting
  order           Int     Order number of the font
    </programlisting>
  </refsect2>
  <refsect2>
  <title>Font Matching</title>
    <para>
Fontconfig performs matching by measuring the distance from a provided
pattern to all of the available fonts in the system.  The closest matching
font is selected.  This ensures that a font will always be returned, but
doesn't ensure that it is anything like the requested pattern.
    </para><para> 
Font matching starts with an application constructed pattern.  The desired
attributes of the resulting font are collected together in a pattern.  Each
property of the pattern can contain one or more values; these are listed in
priority order; matches earlier in the list are considered "closer" than
matches later in the list.
    </para><para>
The initial pattern is modified by applying the list of editing instructions
specific to patterns found in the configuration; each consists of a match
predicate and a set of editing operations.  They are executed in the order
they appeared in the configuration.  Each match causes the associated
sequence of editing operations to be applied.
    </para><para>
After the pattern has been edited, a sequence of default substitutions are
performed to canonicalize the set of available properties; this avoids the
need for the lower layers to constantly provide default values for various
font properties during rendering.
    </para><para>
The canonical font pattern is finally matched against all available fonts.
The distance from the pattern to the font is measured for each of several
properties: foundry, charset, family, lang, spacing, pixelsize, style,
slant, weight, antialias, rasterizer and outline.  This list is in priority
order -- results of comparing earlier elements of this list weigh more
heavily than later elements.
    </para><para>
There is one special case to this rule; family names are split into two
bindings; strong and weak.  Strong family names are given greater precedence
in the match than lang elements while weak family names are given lower
precedence than lang elements.  This permits the document language to drive
font selection when any document specified font is unavailable.
    </para><para>
The pattern representing that font is augmented to include any properties
found in the pattern but not found in the font itself; this permits the
application to pass rendering instructions or any other data through the
matching system.  Finally, the list of editing instructions specific to
fonts found in the configuration are applied to the pattern.  This modified
pattern is returned to the application.
    </para><para>
The return value contains sufficient information to locate and rasterize the
font, including the file name, pixel size and other rendering data.  As
none of the information involved pertains to the FreeType library,
applications are free to use any rasterization engine or even to take
the identified font file and access it directly.
    </para><para>
The match/edit sequences in the configuration are performed in two passes
because there are essentially two different operations necessary -- the
first is to modify how fonts are selected; aliasing families and adding
suitable defaults.  The second is to modify how the selected fonts are
rasterized.  Those must apply to the selected font, not the original pattern
as false matches will often occur.
    </para>
  </refsect2>
  <refsect2><title>Font Names</title>
    <para>
Fontconfig provides a textual representation for patterns that the library
can both accept and generate.  The representation is in three parts, first a
list of family names, second a list of point sizes and finally a list of
additional properties:
    </para>
    <programlisting>
	&lt;families&gt;-&lt;point sizes&gt;:&lt;name1&gt;=&lt;values1&gt;:&lt;name2&gt;=&lt;values2&gt;...
    </programlisting>
    <para>
Values in a list are separated with commas.  The name needn't include either
families or point sizes; they can be elided.  In addition, there are
symbolic constants that simultaneously indicate both a name and a value.
Here are some examples:
    </para>
    <programlisting>
  Name                            Meaning
  ----------------------------------------------------------
  Times-12                        12 point Times Roman
  Times-12:bold                   12 point Times Bold
  Courier:italic                  Courier Italic in the default size
  Monospace:matrix=1 .1 0 1       The users preferred monospace font
                                  with artificial obliquing
    </programlisting>
    <para>
The '\', '-', ':' and ',' characters in family names must be preceded by a
'\' character to avoid having them misinterpreted. Similarly, values
containing '\', '=', '_', ':' and ',' must also have them preceded by a
'\' character. The '\' characters are stripped out of the family name and
values as the font name is read.
    </para>
  </refsect2>
</refsect1>
<refsect1 id="debug"><title>Debugging Applications</title>
  <para>
To help diagnose font and applications problems, fontconfig is built with a
large amount of internal debugging left enabled. It is controlled by means
of the FC_DEBUG environment variable. The value of this variable is
interpreted as a number, and each bit within that value controls different
debugging messages.
  </para>
  <programlisting>
  Name         Value    Meaning
  ---------------------------------------------------------
  MATCH            1    Brief information about font matching
  MATCHV           2    Extensive font matching information
  EDIT             4    Monitor match/test/edit execution
  FONTSET          8    Track loading of font information at startup
  CACHE           16    Watch cache files being written
  CACHEV          32    Extensive cache file writing information
  PARSE           64    (no longer in use)
  SCAN           128    Watch font files being scanned to build caches
  SCANV          256    Verbose font file scanning information
  MEMORY         512    Monitor fontconfig memory usage
  CONFIG        1024    Monitor which config files are loaded
  LANGSET       2048    Dump char sets used to construct lang values
  MATCH2        4096    Display font-matching transformation in patterns
  </programlisting>
  <para>
Add the value of the desired debug levels together and assign that (in
base 10) to the FC_DEBUG environment variable before running the
application. Output from these statements is sent to stdout.
  </para>
</refsect1>
<refsect1><title>Lang Tags</title>
  <para>
Each font in the database contains a list of languages it supports.  This is
computed by comparing the Unicode coverage of the font with the orthography
of each language.  Languages are tagged using an RFC-3066 compatible naming
and occur in two parts -- the ISO 639 language tag followed a hyphen and then
by the ISO 3166 country code.  The hyphen and country code may be elided.
  </para><para>
Fontconfig has orthographies for several languages built into the library.
No provision has been made for adding new ones aside from rebuilding the
library.  It currently supports 122 of the 139 languages named in ISO 639-1,
141 of the languages with two-letter codes from ISO 639-2 and another 30
languages with only three-letter codes.  Languages with both two and three
letter codes are provided with only the two letter code.
  </para><para>
For languages used in multiple territories with radically different
character sets, fontconfig includes per-territory orthographies.  This
includes Azerbaijani, Kurdish, Pashto, Tigrinya and Chinese.
  </para>
</refsect1>
<refsect1><title>Configuration File Format</title>
  <para>
Configuration files for fontconfig are stored in XML format; this
format makes external configuration tools easier to write and ensures that
they will generate syntactically correct configuration files.  As XML
files are plain text, they can also be manipulated by the expert user using
a text editor.
  </para><para>
The fontconfig document type definition resides in the external entity
"fonts.dtd"; this is normally stored in the default font configuration
directory (&confdir;).  Each configuration file should contain the
following structure:
    <programlisting>
	&lt;?xml version="1.0"?&gt;
	&lt;!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"&gt;
	&lt;fontconfig&gt;
	...
	&lt;/fontconfig&gt;
    </programlisting>
  </para>
<refsect2><title><literal>&lt;fontconfig&gt;</literal></title><para>
This is the top level element for a font configuration and can contain
<literal>&lt;dir&gt;</literal>, <literal>&lt;cachedir&gt;</literal>, <literal>&lt;include&gt;</literal>, <literal>&lt;match&gt;</literal> and <literal>&lt;alias&gt;</literal> elements in any order.
  </para></refsect2>
  <refsect2><title><literal>&lt;dir prefix="default" salt=""&gt;</literal></title><para>
This element contains a directory name which will be scanned for font files
to include in the set of available fonts.
  </para><para>
If 'prefix' is set to "default" or "cwd", the current working directory will be added as the path prefix prior to the value. If 'prefix' is set to "xdg", the value in the XDG_DATA_HOME environment variable will be added as the path prefix. please see XDG Base Directory Specification for more details. If 'prefix' is set to "relative", the path of current file will be added prior to the value.
  </para><para>
'salt' property affects to determine cache filename. this is useful for example when having different fonts sets on same path at container and share fonts from host on different font path.
  </para></refsect2>
  <refsect2><title><literal>&lt;cachedir prefix="default"&gt;</literal></title><para>
This element contains a directory name that is supposed to be stored or read
the cache of font information.  If multiple elements are specified in
the configuration file, the directory that can be accessed first in the list
will be used to store the cache files.  If it starts with '~', it refers to
a directory in the users home directory.  If 'prefix' is set to "xdg", the value in the XDG_CACHE_HOME environment variable will be added as the path prefix. please see XDG Base Directory Specification for more details.
The default directory is ``$XDG_CACHE_HOME/fontconfig'' and it contains the cache files
named ``<literal>&lt;hash value&gt;</literal>-<literal>&lt;architecture&gt;</literal>.cache-<literal>&lt;version&gt;</literal>'',
where <literal>&lt;version&gt;</literal> is the fontconfig cache file
version number (currently 7).
  </para></refsect2>
  <refsect2><title><literal>&lt;include ignore_missing="no" prefix="default"&gt;</literal></title><para>
This element contains the name of an additional configuration file or
directory.  If a directory, every file within that directory starting with an
ASCII digit (U+0030 - U+0039) and ending with the string ``.conf'' will be processed in sorted order.  When
the XML datatype is traversed by FcConfigParse, the contents of the file(s)
will also be incorporated into the configuration by passing the filename(s) to
FcConfigLoadAndParse.  If 'ignore_missing' is set to "yes" instead of the
default "no", a missing file or directory will elicit no warning message from
the library.  If 'prefix' is set to "xdg", the value in the XDG_CONFIG_HOME environment variable will be added as the path prefix. please see XDG Base Directory Specification for more details.
  </para></refsect2>
  <refsect2><title><literal>&lt;config&gt;</literal></title><para>
This element provides a place to consolidate additional configuration
information.  <literal>&lt;config&gt;</literal> can contain <literal>&lt;blank&gt;</literal> and <literal>&lt;rescan&gt;</literal> elements in any
order.
  </para></refsect2>
  <refsect2><title><literal>&lt;description domain="fontconfig-conf"&gt;</literal></title><para>
This element is supposed to hold strings which describe what a config is used for.
This string can be translated through gettext. 'domain' needs to be set the proper name to apply then.
fontconfig will tries to retrieve translations with 'domain' from gettext.
  </para></refsect2>
  <refsect2><title><literal>&lt;blank&gt;</literal></title><para>
Fonts often include "broken" glyphs which appear in the encoding but are
drawn as blanks on the screen.  Within the <literal>&lt;blank&gt;</literal> element, place each
Unicode characters which is supposed to be blank in an <literal>&lt;int&gt;</literal> element.
Characters outside of this set which are drawn as blank will be elided from
the set of characters supported by the font.
  </para></refsect2>
  <refsect2><title><literal>&lt;remap-dir prefix="default" as-path="" salt=""&gt;</literal></title><para>
This element contains a directory name where will be mapped
as the path 'as-path' in cached information.
This is useful if the directory name is an alias
(via a bind mount or symlink) to another directory in the system for
which cached font information is likely to exist.
  </para><para>
'salt' property affects to determine cache filename as same as <literal>&lt;dir&gt;</literal> element.
  </para></refsect2>
  <refsect2><title><literal>&lt;reset-dirs /&gt;</literal></title><para>
This element removes all of fonts directories where added by <literal>&lt;dir&gt;</literal> elements.
This is useful to override fonts directories from system to own fonts directories only.
  </para></refsect2>
  <refsect2><title><literal>&lt;rescan&gt;</literal></title><para>
The <literal>&lt;rescan&gt;</literal> element holds an <literal>&lt;int&gt;</literal> element which indicates the default
interval between automatic checks for font configuration changes.
Fontconfig will validate all of the configuration files and directories and
automatically rebuild the internal datastructures when this interval passes.
  </para></refsect2>
  <refsect2><title><literal>&lt;selectfont&gt;</literal></title><para>
This element is used to black/white list fonts from being listed or matched
against.  It holds acceptfont and rejectfont elements.
  </para></refsect2>
  <refsect2><title><literal>&lt;acceptfont&gt;</literal></title><para>
Fonts matched by an acceptfont element are "whitelisted"; such fonts are
explicitly included in the set of fonts used to resolve list and match
requests; including them in this list protects them from being "blacklisted"
by a rejectfont element.  Acceptfont elements include glob and pattern
elements which are used to match fonts.
  </para></refsect2>
  <refsect2><title><literal>&lt;rejectfont&gt;</literal></title><para>
Fonts matched by an rejectfont element are "blacklisted"; such fonts are
excluded from the set of fonts used to resolve list and match requests as if
they didn't exist in the system.  Rejectfont elements include glob and
pattern elements which are used to match fonts.
  </para></refsect2>
  <refsect2><title><literal>&lt;glob&gt;</literal></title><para>
Glob elements hold shell-style filename matching patterns (including ? and
*) which match fonts based on their complete pathnames.  This can be used to
exclude a set of directories (/usr/share/fonts/uglyfont*), or particular
font file types (*.pcf.gz), but the latter mechanism relies rather heavily
on filenaming conventions which can't be relied upon.  Note that globs
only apply to directories, not to individual fonts.
  </para></refsect2>
  <refsect2><title><literal>&lt;pattern&gt;</literal></title><para>
Pattern elements perform list-style matching on incoming fonts; that is,
they hold a list of elements and associated values.  If all of those
elements have a matching value, then the pattern matches the font.  This can
be used to select fonts based on attributes of the font (scalable, bold,
etc), which is a more reliable mechanism than using file extensions.
Pattern elements include patelt elements.
  </para></refsect2>
  <refsect2><title><literal>&lt;patelt name="property"&gt;</literal></title><para>
Patelt elements hold a single pattern element and list of values.  They must
have a 'name' attribute which indicates the pattern element name.  Patelt
elements include int, double, string, matrix, bool, charset and const
elements.
  </para></refsect2>
  <refsect2><title><literal>&lt;match target="pattern"&gt;</literal></title><para>
This element holds first a (possibly empty) list of <literal>&lt;test&gt;</literal> elements and then
a (possibly empty) list of <literal>&lt;edit&gt;</literal> elements.  Patterns which match all of the
tests are subjected to all the edits.  If 'target' is set to "font" instead
of the default "pattern", then this element applies to the font name
resulting from a match rather than a font pattern to be matched. If 'target'
is set to "scan", then this element applies when the font is scanned to
build the fontconfig database.
  </para></refsect2>
  <refsect2><title><literal>&lt;test qual="any" name="property" target="default" compare="eq"&gt;</literal></title><para>
This element contains a single value which is compared with the target
('pattern', 'font', 'scan' or 'default') property "property" (substitute any of the property names seen 
above). 'compare' can be one of "eq", "not_eq", "less", "less_eq", "more", "more_eq", "contains" or
"not_contains".  'qual' may either be the default, "any", in which case the match
succeeds if any value associated with the property matches the test value, or
"all", in which case all of the values associated with the property must
match the test value.  'ignore-blanks' takes a boolean value. if 'ignore-blanks' is set "true", any blanks in the string will be ignored on its comparison. this takes effects only when compare="eq" or compare="not_eq".
When used in a &lt;match target="font"&gt; element,
the target= attribute in the &lt;test&gt; element selects between matching
the original pattern or the font.  "default" selects whichever target the
outer &lt;match&gt; element has selected.
  </para></refsect2>
  <refsect2><title><literal>&lt;edit name="property" mode="assign" binding="weak"&gt;</literal></title><para>
This element contains a list of expression elements (any of the value or
operator elements).  The expression elements are evaluated at run-time and
modify the property "property".  The modification depends on whether
"property" was matched by one of the associated <literal>&lt;test&gt;</literal> elements, if so, the
modification may affect the first matched value.  Any values inserted into
the property are given the indicated binding ("strong", "weak" or "same")
with "same" binding using the value from the matched pattern element.
'mode' is one of:
    <programlisting>
  Mode                    With Match              Without Match
  ---------------------------------------------------------------------
  "assign"                Replace matching value  Replace all values
  "assign_replace"        Replace all values      Replace all values
  "prepend"               Insert before matching  Insert at head of list
  "prepend_first"         Insert at head of list  Insert at head of list
  "append"                Append after matching   Append at end of list
  "append_last"           Append at end of list   Append at end of list
  "delete"                Delete matching value   Delete all values
  "delete_all"            Delete all values       Delete all values
    </programlisting>
  </para></refsect2>
  <refsect2><title><literal>&lt;int&gt;</literal>, <literal>&lt;double&gt;</literal>, <literal>&lt;string&gt;</literal>, <literal>&lt;bool&gt;</literal></title><para>
These elements hold a single value of the indicated type.  <literal>&lt;bool&gt;</literal>
elements hold either true or false.  An important limitation exists in
the parsing of floating point numbers -- fontconfig requires that
the mantissa start with a digit, not a decimal point, so insert a leading
zero for purely fractional values (e.g. use 0.5 instead of .5 and -0.5
instead of -.5).
  </para></refsect2>
  <refsect2><title><literal>&lt;matrix&gt;</literal></title><para>
This element holds four numerical expressions of an affine transformation.
At their simplest these will be four <literal>&lt;double&gt;</literal> elements
but they can also be more involved expressions.
  </para></refsect2>
  <refsect2><title><literal>&lt;range&gt;</literal></title><para>
This element holds the two <literal>&lt;int&gt;</literal> elements of a range
representation.
  </para></refsect2>
  <refsect2><title><literal>&lt;charset&gt;</literal></title><para>
This element holds at least one <literal>&lt;int&gt;</literal> element of
an Unicode code point or more.
  </para></refsect2>
  <refsect2><title><literal>&lt;langset&gt;</literal></title><para>
This element holds at least one <literal>&lt;string&gt;</literal> element of
a RFC-3066-style languages or more.
  </para></refsect2>
  <refsect2><title><literal>&lt;name&gt;</literal></title><para>
Holds a property name.  Evaluates to the first value from the property of
the pattern.  If the 'target' attribute is not present, it will default to
'default', in which case the property is returned from the font pattern
during a target="font" match, and to the pattern during a target="pattern"
match.  The attribute can also take the values 'font' or 'pattern' to
explicitly choose which pattern to use.  It is an error to use a target
of 'font' in a match that has target="pattern".
  </para></refsect2>
  <refsect2><title><literal>&lt;const&gt;</literal></title><para>
Holds the name of a constant; these are always integers and serve as
symbolic names for common font values:
    <programlisting>
  Constant        Property        Value
  -------------------------------------
  thin            weight          0
  extralight      weight          40
  ultralight      weight          40
  light           weight          50
  demilight       weight          55
  semilight       weight          55
  book            weight          75
  regular         weight          80
  normal          weight          80
  medium          weight          100
  demibold        weight          180
  semibold        weight          180
  bold            weight          200
  extrabold       weight          205
  black           weight          210
  heavy           weight          210
  roman           slant           0
  italic          slant           100
  oblique         slant           110
  ultracondensed  width           50
  extracondensed  width           63
  condensed       width           75
  semicondensed   width           87
  normal          width           100
  semiexpanded    width           113
  expanded        width           125
  extraexpanded   width           150
  ultraexpanded   width           200
  proportional    spacing         0
  dual            spacing         90
  mono            spacing         100
  charcell        spacing         110
  unknown         rgba            0
  rgb             rgba            1
  bgr             rgba            2
  vrgb            rgba            3
  vbgr            rgba            4
  none            rgba            5
  lcdnone         lcdfilter       0
  lcddefault      lcdfilter       1
  lcdlight        lcdfilter       2
  lcdlegacy       lcdfilter       3
  hintnone        hintstyle       0
  hintslight      hintstyle       1
  hintmedium      hintstyle       2
  hintfull        hintstyle       3
    </programlisting>
      </para>
    </refsect2>
  <refsect2>
      <title><literal>&lt;or&gt;</literal>, <literal>&lt;and&gt;</literal>, <literal>&lt;plus&gt;</literal>, <literal>&lt;minus&gt;</literal>, <literal>&lt;times&gt;</literal>, <literal>&lt;divide&gt;</literal></title>
      <para>
These elements perform the specified operation on a list of expression
elements.  <literal>&lt;or&gt;</literal> and <literal>&lt;and&gt;</literal> are boolean, not bitwise.
      </para>
    </refsect2>
  <refsect2>
    <title><literal>&lt;eq&gt;</literal>, <literal>&lt;not_eq&gt;</literal>, <literal>&lt;less&gt;</literal>, <literal>&lt;less_eq&gt;</literal>, <literal>&lt;more&gt;</literal>, <literal>&lt;more_eq&gt;</literal>, <literal>&lt;contains&gt;</literal>, <literal>&lt;not_contains</literal></title>
    <para>
These elements compare two values, producing a boolean result.
  </para></refsect2>
  <refsect2><title><literal>&lt;not&gt;</literal></title><para>
Inverts the boolean sense of its one expression element
  </para></refsect2>
  <refsect2><title><literal>&lt;if&gt;</literal></title><para>
This element takes three expression elements; if the value of the first is
true, it produces the value of the second, otherwise it produces the value
of the third.
  </para></refsect2>
  <refsect2><title><literal>&lt;alias&gt;</literal></title><para>
Alias elements provide a shorthand notation for the set of common match
operations needed to substitute one font family for another.  They contain a
<literal>&lt;family&gt;</literal> element followed by optional <literal>&lt;prefer&gt;</literal>, <literal>&lt;accept&gt;</literal> and <literal>&lt;default&gt;</literal>
elements.  Fonts matching the <literal>&lt;family&gt;</literal> element are edited to prepend the
list of <literal>&lt;prefer&gt;</literal>ed families before the matching <literal>&lt;family&gt;</literal>, append the
<literal>&lt;accept&gt;</literal>able families after the matching <literal>&lt;family&gt;</literal> and append the <literal>&lt;default&gt;</literal>
families to the end of the family list.
  </para></refsect2>
  <refsect2><title><literal>&lt;family&gt;</literal></title><para>
Holds a single font family name
  </para></refsect2>
  <refsect2><title><literal>&lt;prefer&gt;</literal>, <literal>&lt;accept&gt;</literal>, <literal>&lt;default&gt;</literal></title><para>
These hold a list of <literal>&lt;family&gt;</literal> elements to be used by the <literal>&lt;alias&gt;</literal> element.
  </para></refsect2>
</refsect1>
<refsect1><title>EXAMPLE CONFIGURATION FILE</title>
  <refsect2><title>System configuration file</title>
    <para>
This is an example of a system-wide configuration file
    </para>
    <programlisting>
&lt;?xml version="1.0"?&gt;
&lt;!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"&gt;
&lt;!-- &confdir;/fonts.conf file to configure system font access --&gt;
&lt;fontconfig&gt;
&lt;!-- 
	Find fonts in these directories
--&gt;
&lt;dir&gt;/usr/share/fonts&lt;/dir&gt;
&lt;dir&gt;/usr/X11R6/lib/X11/fonts&lt;/dir&gt;

&lt;!--
	Accept deprecated 'mono' alias, replacing it with 'monospace'
--&gt;
&lt;match target="pattern"&gt;
	&lt;test qual="any" name="family"&gt;&lt;string&gt;mono&lt;/string&gt;&lt;/test&gt;
	&lt;edit name="family" mode="assign"&gt;&lt;string&gt;monospace&lt;/string&gt;&lt;/edit&gt;
&lt;/match&gt;

&lt;!--
	Names not including any well known alias are given 'sans-serif'
--&gt;
&lt;match target="pattern"&gt;
	&lt;test qual="all" name="family" compare="not_eq"&gt;&lt;string&gt;sans-serif&lt;/string&gt;&lt;/test&gt;
	&lt;test qual="all" name="family" compare="not_eq"&gt;&lt;string&gt;serif&lt;/string&gt;&lt;/test&gt;
	&lt;test qual="all" name="family" compare="not_eq"&gt;&lt;string&gt;monospace&lt;/string&gt;&lt;/test&gt;
	&lt;edit name="family" mode="append_last"&gt;&lt;string&gt;sans-serif&lt;/string&gt;&lt;/edit&gt;
&lt;/match&gt;

&lt;!--
	Load per-user customization file, but don't complain
	if it doesn't exist
--&gt;
&lt;include ignore_missing="yes" prefix="xdg"&gt;fontconfig/fonts.conf&lt;/include&gt;

&lt;!--
	Load local customization files, but don't complain
	if there aren't any
--&gt;
&lt;include ignore_missing="yes"&gt;conf.d&lt;/include&gt;
&lt;include ignore_missing="yes"&gt;local.conf&lt;/include&gt;

&lt;!--
	Alias well known font names to available TrueType fonts.
	These substitute TrueType faces for similar Type1
	faces to improve screen appearance.
--&gt;
&lt;alias&gt;
	&lt;family&gt;Times&lt;/family&gt;
	&lt;prefer&gt;&lt;family&gt;Times New Roman&lt;/family&gt;&lt;/prefer&gt;
	&lt;default&gt;&lt;family&gt;serif&lt;/family&gt;&lt;/default&gt;
&lt;/alias&gt;
&lt;alias&gt;
	&lt;family&gt;Helvetica&lt;/family&gt;
	&lt;prefer&gt;&lt;family&gt;Arial&lt;/family&gt;&lt;/prefer&gt;
	&lt;default&gt;&lt;family&gt;sans&lt;/family&gt;&lt;/default&gt;
&lt;/alias&gt;
&lt;alias&gt;
	&lt;family&gt;Courier&lt;/family&gt;
	&lt;prefer&gt;&lt;family&gt;Courier New&lt;/family&gt;&lt;/prefer&gt;
	&lt;default&gt;&lt;family&gt;monospace&lt;/family&gt;&lt;/default&gt;
&lt;/alias&gt;

&lt;!--
	Provide required aliases for standard names
	Do these after the users configuration file so that
	any aliases there are used preferentially
--&gt;
&lt;alias&gt;
	&lt;family&gt;serif&lt;/family&gt;
	&lt;prefer&gt;&lt;family&gt;Times New Roman&lt;/family&gt;&lt;/prefer&gt;
&lt;/alias&gt;
&lt;alias&gt;
	&lt;family&gt;sans&lt;/family&gt;
	&lt;prefer&gt;&lt;family&gt;Arial&lt;/family&gt;&lt;/prefer&gt;
&lt;/alias&gt;
&lt;alias&gt;
	&lt;family&gt;monospace&lt;/family&gt;
	&lt;prefer&gt;&lt;family&gt;Andale Mono&lt;/family&gt;&lt;/prefer&gt;
&lt;/alias&gt;

&lt;--
	The example of the requirements of OR operator;
	If the 'family' contains 'Courier New' OR 'Courier'
	add 'monospace' as the alternative
--&gt;
&lt;match target="pattern"&gt;
	&lt;test name="family" compare="eq"&gt;
		&lt;string&gt;Courier New&lt;/string&gt;
	&lt;/test&gt;
	&lt;edit name="family" mode="prepend"&gt;
		&lt;string&gt;monospace&lt;/string&gt;
	&lt;/edit&gt;
&lt;/match&gt;
&lt;match target="pattern"&gt;
	&lt;test name="family" compare="eq"&gt;
		&lt;string&gt;Courier&lt;/string&gt;
	&lt;/test&gt;
	&lt;edit name="family" mode="prepend"&gt;
		&lt;string&gt;monospace&lt;/string&gt;
	&lt;/edit&gt;
&lt;/match&gt;

&lt;/fontconfig&gt;
    </programlisting>
  </refsect2>
  <refsect2><title>User configuration file</title>
    <para>
This is an example of a per-user configuration file that lives in
$XDG_CONFIG_HOME/fontconfig/fonts.conf
    </para>
    <programlisting>
&lt;?xml version="1.0"?&gt;
&lt;!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"&gt;
&lt;!-- $XDG_CONFIG_HOME/fontconfig/fonts.conf for per-user font configuration --&gt;
&lt;fontconfig&gt;

&lt;!--
	Private font directory
--&gt;
&lt;dir prefix="xdg"&gt;fonts&lt;/dir&gt;

&lt;!--
	use rgb sub-pixel ordering to improve glyph appearance on
	LCD screens.  Changes affecting rendering, but not matching
	should always use target="font".
--&gt;
&lt;match target="font"&gt;
	&lt;edit name="rgba" mode="assign"&gt;&lt;const&gt;rgb&lt;/const&gt;&lt;/edit&gt;
&lt;/match&gt;
&lt;!--
	use WenQuanYi Zen Hei font when serif is requested for Chinese
--&gt;
&lt;match&gt;
	&lt;!--
		If you don't want to use WenQuanYi Zen Hei font for zh-tw etc,
		you can use zh-cn instead of zh.
		Please note, even if you set zh-cn, it still matches zh.
		if you don't like it, you can use compare="eq"
		instead of compare="contains".
	--&gt;
	&lt;test name="lang" compare="contains"&gt;
		&lt;string&gt;zh&lt;/string&gt;
	&lt;/test&gt;
	&lt;test name="family"&gt;
		&lt;string&gt;serif&lt;/string&gt;
	&lt;/test&gt;
	&lt;edit name="family" mode="prepend"&gt;
		&lt;string&gt;WenQuanYi Zen Hei&lt;/string&gt;
	&lt;/edit&gt;
&lt;/match&gt;
&lt;!--
	use VL Gothic font when sans-serif is requested for Japanese
--&gt;
&lt;match&gt;
	&lt;test name="lang" compare="contains"&gt;
		&lt;string&gt;ja&lt;/string&gt;
	&lt;/test&gt;
	&lt;test name="family"&gt;
		&lt;string&gt;sans-serif&lt;/string&gt;
	&lt;/test&gt;
	&lt;edit name="family" mode="prepend"&gt;
		&lt;string&gt;VL Gothic&lt;/string&gt;
	&lt;/edit&gt;
&lt;/match&gt;
&lt;/fontconfig&gt;
    </programlisting>
  </refsect2>
</refsect1>
<refsect1><title>Files</title>
  <para>
<emphasis>fonts.conf</emphasis>
contains configuration information for the fontconfig library
consisting of directories to look at for font information as well as
instructions on editing program specified font patterns before attempting to
match the available fonts.  It is in XML format.
  </para>
  <para>
<emphasis>conf.d</emphasis>
is the conventional name for a directory of additional configuration files
managed by external applications or the local administrator.  The
filenames starting with decimal digits are sorted in lexicographic order
and used as additional configuration files.  All of these files are in XML
format.  The master fonts.conf file references this directory in an 
&lt;include&gt; directive.
  </para>
  <para>
<emphasis>fonts.dtd</emphasis>
is a DTD that describes the format of the configuration files.
  </para>
  <para>
<emphasis>$XDG_CONFIG_HOME/fontconfig/conf.d</emphasis> and <emphasis>~/.fonts.conf.d</emphasis>
is the conventional name for a per-user directory of (typically
auto-generated) configuration files, although the
actual location is specified in the global fonts.conf file. please note that ~/.fonts.conf.d is deprecated now. it will not be read by default in the future version.
  </para>
  <para>
<emphasis>$XDG_CONFIG_HOME/fontconfig/fonts.conf</emphasis> and <emphasis>~/.fonts.conf</emphasis>
is the conventional location for per-user font configuration, although the
actual location is specified in the global fonts.conf file. please note that ~/.fonts.conf is deprecated now. it will not be read by default in the future version.
  </para>
  <para>
<emphasis>$XDG_CACHE_HOME/fontconfig/*.cache-*</emphasis> and <emphasis> ~/.fontconfig/*.cache-*</emphasis>
is the conventional repository of font information that isn't found in the
per-directory caches.  This file is automatically maintained by fontconfig. please note that ~/.fontconfig/*.cache-* is deprecated now. it will not be read by default in the future version.
  </para>
</refsect1>
<refsect1><title>Environment variables</title>
  <para>
<emphasis>FONTCONFIG_FILE</emphasis>
is used to override the default configuration file.
  </para>
  <para>
<emphasis>FONTCONFIG_PATH</emphasis>
is used to override the default configuration directory.
  </para>
  <para>
<emphasis>FONTCONFIG_SYSROOT</emphasis>
is used to set a default sysroot directory.
  </para>
  <para>
<emphasis>FC_DEBUG</emphasis>
is used to output the detailed debugging messages. see <link linkend="debug">Debugging Applications</link> section for more details.
  </para>
  <para>
<emphasis>FC_DBG_MATCH_FILTER</emphasis>
is used to filter out the patterns. this takes a comma-separated list of object names and effects only when FC_DEBUG has MATCH2. see <link linkend="debug">Debugging Applications</link> section for more details.
  </para>
  <para>
<emphasis>FC_LANG</emphasis>
is used to specify the default language as the weak binding in the query. if this isn't set, the default language will be determined from current locale.
  </para>
  <para>
<emphasis>FONTCONFIG_USE_MMAP</emphasis>
is used to control the use of mmap(2) for the cache files if available. this take a boolean value. fontconfig will checks if the cache files are stored on the filesystem that is safe to use mmap(2). explicitly setting this environment variable will causes skipping this check and enforce to use or not use mmap(2) anyway.
  </para>
  <para>
<emphasis>SOURCE_DATE_EPOCH</emphasis>
is used to ensure <literal>fc-cache(1)</literal> generates files in a deterministic manner in order to support reproducible builds. When set to a numeric representation of UNIX timestamp, fontconfig will prefer this value over using the modification timestamps of the input files in order to identify which cache files require regeneration. If <literal>SOURCE_DATE_EPOCH</literal> is not set (or is newer than the mtime of the directory), the existing behaviour is unchanged.
  </para>
</refsect1>
<refsect1><title>See Also</title>
  <para>
fc-cat(1), fc-cache(1), fc-list(1), fc-match(1), fc-query(1), <ulink url="https://reproducible-builds.org/specs/source-date-epoch/">SOURCE_DATE_EPOCH</ulink>.
  </para>
</refsect1>
<refsect1><title>Version</title>
	    <para>
Fontconfig version &version;
	    </para>
</refsect1>
</refentry>