FONTS-CONF(5)                                                                                                         FONTS-CONF(5)

       fonts.conf - Font configuration files


       Fontconfig is a library designed to provide system-wide font configuration, customization and application access.

       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.

       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 gen‐
       erating 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.

       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.

       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.  Cen‐
       tralizing font configuration will simplify and regularize font installation and customization.

       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.

         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

       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 any‐
       thing like the requested pattern.

       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.

       The initial pattern is modified by applying the list of editing instructions specific to patterns found  in  the  configura‐
       tion;  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.

       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 dur‐
       ing rendering.

       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, an‐
       tialias, rasterizer and outline.  This list is in priority order -- results of comparing earlier elements of this list weigh
       more heavily than later elements.

       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  ele‐
       ments.  This permits the document language to drive font selection when any document specified font is unavailable.

       The pattern representing that font is augmented to include any properties found in the pattern but not found in the font it‐
       self; 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.

       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.

       The match/edit sequences in the configuration are performed in two passes because there are essentially two different opera‐
       tions  necessary -- the first is to modify how fonts are selected; aliasing families and adding suitable defaults.  The sec‐
       ond 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.

       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:

            <families>-<point sizes>:<name1>=<values1>:<name2>=<values2>...

       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:

         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

       The  '\',  '-',  ':'  and  ',' characters in family names must be preceded by a '\' character to avoid having them misinter‐
       preted. 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.

       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.

         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

       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.

       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.

       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.

       For languages used in multiple territories with radically different character sets, fontconfig  includes  per-territory  or‐
       thographies.  This includes Azerbaijani, Kurdish, Pashto, Tigrinya and Chinese.

       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.

       The  fontconfig  document type definition resides in the external entity "fonts.dtd"; this is normally stored in the default
       font configuration directory (/etc/fonts).  Each configuration file should contain the following structure:

            <?xml version="1.0"?>
            <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">

       This is the top level element for a font configuration and can contain <dir>, <cachedir>, <include>, <match> and <alias> el‐
       ements in any order.

       This element contains a directory name which will be scanned for font files to include in the set of available fonts.

       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.

       '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.

       This element contains a directory name that is supposed to be stored or read the cache of font information.  If multiple el‐
       ements 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  Speci‐
       fication  for  more  details.  The default directory is ``$XDG_CACHE_HOME/fontconfig'' and it contains the cache files named
       ``<hash value>-<architecture>.cache-<version>'', where <version> is the fontconfig cache file version number (currently 7).

       This element contains the name of an additional configuration file or directory.  If a directory, every file within that di‐
       rectory  starting with an ASCII digit (U+0030 - U+0039) and ending with the string ``.conf'' will be processed in sorted or‐
       der.  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 de‐
       fault "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 Specifica‐
       tion for more details.

       This element provides a place to consolidate additional configuration information.  <config> can contain <blank>  and  <res‐
       can> elements in any order.

       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  'do‐
       main' from gettext.

       Fonts  often include "broken" glyphs which appear in the encoding but are drawn as blanks on the screen.  Within the <blank>
       element, place each Unicode characters which is supposed to be blank in an <int> element.  Characters outside  of  this  set
       which are drawn as blank will be elided from the set of characters supported by the font.

       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 infor‐
       mation is likely to exist.

       'salt' property affects to determine cache filename as same as <dir> element.

       This  element  removes all of fonts directories where added by <dir> elements.  This is useful to override fonts directories
       from system to own fonts directories only.

       The <rescan> element holds an <int> element which indicates the default interval between automatic checks for font  configu‐
       ration  changes.   Fontconfig will validate all of the configuration files and directories and automatically rebuild the in‐
       ternal datastructures when this interval passes.

       This element is used to black/white list fonts from being listed or matched against.  It holds acceptfont and rejectfont el‐

       Fonts matched by an acceptfont element are "whitelisted"; such fonts are explicitly included in the set of fonts used to re‐
       solve 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.

       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.

       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.

       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 el‐
       ements include patelt elements.

       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.

       This element holds first a (possibly empty) list of <test> elements and then a (possibly empty)  list  of  <edit>  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.

       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  <match target="font"> element, the target= attribute in the <test> element selects between matching the original pat‐
       tern or the font.  "default" selects whichever target the outer <match> element has selected.

       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 <test> 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:

         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

       These elements hold a single value of the indicated type.  <bool> elements hold either true or false.  An important  limita‐
       tion exists in the parsing of floating point numbers -- fontconfig requires that the mantissa start with a digit, not a dec‐
       imal point, so insert a leading zero for purely fractional values (e.g. use 0.5 instead of .5 and -0.5 instead of -.5).

       This element holds four numerical expressions of an affine transformation.  At their simplest these will  be  four  <double>
       elements but they can also be more involved expressions.

       This element holds the two <int> elements of a range representation.

       This element holds at least one <int> element of an Unicode code point or more.

       This element holds at least one <string> element of a RFC-3066-style languages or more.

       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".

       Holds the name of a constant; these are always integers and serve as symbolic names for common font values:

         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

   <OR>, <AND>, <PLUS>, <MINUS>, <TIMES>, <DIVIDE>
       These elements perform the specified operation on a list of expression elements.  <or> and <and> are boolean, not bitwise.

       These elements compare two values, producing a boolean result.

       Inverts the boolean sense of its one expression element

       This element takes three expression elements; if the value of the first is true, it produces the value of the second, other‐
       wise it produces the value of the third.

       Alias  elements provide a shorthand notation for the set of common match operations needed to substitute one font family for
       another.  They contain a <family> element followed by optional <prefer>, <accept> and <default>  elements.   Fonts  matching
       the  <family>  element  are  edited to prepend the list of <prefer>ed families before the matching <family>, append the <ac‐
       cept>able families after the matching <family> and append the <default> families to the end of the family list.

       Holds a single font family name

       These hold a list of <family> elements to be used by the <alias> element.

       This is an example of a system-wide configuration file

       <?xml version="1.0"?>
       <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
       <!-- /etc/fonts/fonts.conf file to configure system font access -->
            Find fonts in these directories

            Accept deprecated 'mono' alias, replacing it with 'monospace'
       <match target="pattern">
            <test qual="any" name="family"><string>mono</string></test>
            <edit name="family" mode="assign"><string>monospace</string></edit>

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

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

            Load local customization files, but don't complain
            if there aren't any
       <include ignore_missing="yes">conf.d</include>
       <include ignore_missing="yes">local.conf</include>

            Alias well known font names to available TrueType fonts.
            These substitute TrueType faces for similar Type1
            faces to improve screen appearance.
            <prefer><family>Times New Roman</family></prefer>
            <prefer><family>Courier New</family></prefer>

            Provide required aliases for standard names
            Do these after the users configuration file so that
            any aliases there are used preferentially
            <prefer><family>Times New Roman</family></prefer>
            <prefer><family>Andale Mono</family></prefer>

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


       This is an example of a per-user configuration file that lives in $XDG_CONFIG_HOME/fontconfig/fonts.conf

       <?xml version="1.0"?>
       <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
       <!-- $XDG_CONFIG_HOME/fontconfig/fonts.conf for per-user font configuration -->

            Private font directory
       <dir prefix="xdg">fonts</dir>

            use rgb sub-pixel ordering to improve glyph appearance on
            LCD screens.  Changes affecting rendering, but not matching
            should always use target="font".
       <match target="font">
            <edit name="rgba" mode="assign"><const>rgb</const></edit>
            use WenQuanYi Zen Hei font when serif is requested for Chinese
                 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".
            <test name="lang" compare="contains">
            <test name="family">
            <edit name="family" mode="prepend">
                 <string>WenQuanYi Zen Hei</string>
            use VL Gothic font when sans-serif is requested for Japanese
            <test name="lang" compare="contains">
            <test name="family">
            <edit name="family" mode="prepend">
                 <string>VL Gothic</string>

       fonts.conf contains configuration information for the fontconfig library consisting of directories to look at for  font  in‐
       formation as well as instructions on editing program specified font patterns before attempting to match the available fonts.
       It is in XML format.

       conf.d 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 <in‐
       clude> directive.

       fonts.dtd is a DTD that describes the format of the configuration files.

       $XDG_CONFIG_HOME/fontconfig/conf.d and ~/.fonts.conf.d 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.

       $XDG_CONFIG_HOME/fontconfig/fonts.conf  and  ~/.fonts.conf is the conventional location for per-user font configuration, al‐
       though 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.

       $XDG_CACHE_HOME/fontconfig/*.cache-*  and   ~/.fontconfig/*.cache-*  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  ~/.fontcon‐
       fig/*.cache-* is deprecated now. it will not be read by default in the future version.

       FONTCONFIG_FILE is used to override the default configuration file.

       FONTCONFIG_PATH is used to override the default configuration directory.

       FONTCONFIG_SYSROOT is used to set a default sysroot directory.

       FC_DEBUG is used to output the detailed debugging messages. see Debugging Applications section for more details.

       FC_DBG_MATCH_FILTER  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 Debugging Applications section for more details.

       FC_LANG 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.

       FONTCONFIG_USE_MMAP is used to control the use of mmap(2) for the cache files if available. this take a boolean value. font‐
       config will checks if the cache files are stored on the filesystem that is safe to use mmap(2). explicitly setting this  en‐
       vironment variable will causes skipping this check and enforce to use or not use mmap(2) anyway.

       SOURCE_DATE_EPOCH  is  used to ensure fc-cache(1) 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  modifica‐
       tion  timestamps of the input files in order to identify which cache files require regeneration. If SOURCE_DATE_EPOCH is not
       set (or is newer than the mtime of the directory), the existing behaviour is unchanged.

       fc-cat(1),    fc-cache(1),    fc-list(1),    fc-match(1),    fc-query(1),    SOURCE_DATE_EPOCH    <URL:https://reproducible->.

       Fontconfig version 2.14.1

                                                          23 February 2023                                            FONTS-CONF(5)