Fix doc typo

[fontconfig.git] / doc / fcformat.fncs

/*
 * fontconfig/doc/fcformat.fncs
 *
 * Copyright © 2008 Behdad Esfahbod
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that
 * copyright notice and this permission notice appear in supporting
 * documentation, and that the name of Keith Packard not be used in
 * advertising or publicity pertaining to distribution of the software without
 * specific, written prior permission.  Keith Packard makes no
 * representations about the suitability of this software for any purpose.  It
 * is provided "as is" without express or implied warranty.
 *
 * THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

@RET@		FcChar8 *
@FUNC@		FcPatternFormat
@TYPE1@		FcPattern *			@ARG1@		pat
@TYPE2@		const FcChar8 *			@ARG2@		format
@PURPOSE@	Format a pattern into a string according to a format specifier
@DESC@

Converts given pattern <parameter>pat</parameter> into text described by
the format specifier <parameter>format</parameter>.
The return value refers to newly allocated memory which should be freed by the
caller using free(), or NULL if <parameter>format</parameter> is invalid.

</para><para>

The format is loosely modelled after printf-style format string.
The format string is composed of zero or more  directives: ordinary
characters (not "%"), which are copied unchanged to the output stream;
and tags which are interpreted to construct text from the pattern in a
variety of ways (explained below).
Special characters can be escaped
using backslash.  C-string style special characters like \n and \r are
also supported (this is useful when the format string is not a C string
literal).
It is advisable to always escape curly braces that
are meant to be copied to the output as ordinary characters.

</para><para>

Each tag is introduced by the character "%",
followed by an optional minimum field width,
followed by tag contents in curly braces ({}).
If the minimum field width value is provided the tag
will be expanded and the result padded to achieve the minimum width.
If the minimum field width is positive, the padding will right-align
the text.  Negative field width will left-align.
The rest of this section describes various supported tag contents
and their expansion.

</para><para>

A <firstterm>simple</firstterm> tag
is one where the content is an identifier.  When simple
tags are expanded, the named identifier will be looked up in
<parameter>pattern</parameter> and the resulting list of values returned,
joined together using comma.  For example, to print the family name and style the
pattern, use the format "%{family} %{style}\n".  To extend the family column
to forty characters use "%-40{family}%{style}\n".

</para><para>

Simple tags expand to list of all values for an element.  To only choose
one of the values, one can index using the syntax "%{elt[idx]}".  For example,
to get the first family name only, use "%{family[0]}".

</para><para>

If a simple tag ends with "=" and the element is found in the pattern, the
name of the element followed by "=" will be output before the list of values.
For example, "%{weight=}" may expand to the string "weight=80".  Or to the empty
string if <parameter>pattern</parameter> does not have weight set.

</para><para>

If a simple tag starts with ":" and the element is found in the pattern, ":"
will be printed first.  For example, combining this with the =, the format
"%{:weight=}" may expand to ":weight=80" or to the empty string
if <parameter>pattern</parameter> does not have weight set.

</para><para>

If a simple tag contains the string ":-", the rest of the the tag contents
will be used as a default string.  The default string is output if the element
is not found in the pattern.  For example, the format
"%{:weight=:-123}" may expand to ":weight=80" or to the string
":weight=123" if <parameter>pattern</parameter> does not have weight set.

</para><para>

A <firstterm>count</firstterm> tag
is one that starts with the character "#" followed by an element
name, and expands to the number of values for the element in the pattern.
For example, "%{#family}" expands to the number of family names
<parameter>pattern</parameter> has set, which may be zero.

</para><para>

A <firstterm>sub-expression</firstterm> tag
is one that expands a sub-expression.  The tag contents
are the sub-expression to expand placed inside another set of curly braces.
Sub-expression tags are useful for aligning an entire sub-expression, or to
apply converters (explained later) on an entire sub-expression.
For example, the format "%40{{%{family} %{style}}}" expands the sub-expression
to construct the family name followed by the style, then takes the entire
string and pads it on the left to be at least forty characters.

</para><para>

A <firstterm>filter-out</firstterm> tag
is one starting with the character "-" followed by a
comma-separated list of element names, followed by a sub-expression enclosed
in curly braces.  The sub-expression will be expanded but with a pattern that
has the listed elements removed from it.
For example, the format "%{-size,pixelsize{sub-expr}}" will expand "sub-expr"
with <parameter>pattern</parameter> sans the size and pixelsize elements.

</para><para>

A <firstterm>filter-in</firstterm> tag
is one starting with the character "+" followed by a
comma-separated list of element names, followed by a sub-expression enclosed
in curly braces.  The sub-expression will be expanded but with a pattern that
only has the listed elements from the surrounding pattern.
For example, the format "%{+family,familylang{sub-expr}}" will expand "sub-expr"
with a sub-pattern consisting only the family and family lang elements of
<parameter>pattern</parameter>.

</para><para>

A <firstterm>conditional</firstterm> tag
is one starting with the character "?" followed by a
comma-separated list of element conditions, followed by two sub-expression
enclosed in curly braces.  An element condition can be an element name,
in which case it tests whether the element is defined in pattern, or
the character "!" followed by an element name, in which case the test
is negated.  The conditional passes if all the element conditions pass.
The tag expands the first sub-expression if the conditional passes, and
expands the second sub-expression otherwise.
For example, the format "%{?size,dpi,!pixelsize{pass}{fail}}" will expand
to "pass" if <parameter>pattern</parameter> has size and dpi elements but
no pixelsize element, and to "fail" otherwise.

</para><para>

An <firstterm>enumerate</firstterm> tag
is one starting with the string "[]" followed by a
comma-separated list of element names, followed by a sub-expression enclosed
in curly braces.  The list of values for the named elements are walked in
parallel and the sub-expression expanded each time with a pattern just having
a single value for those elements, starting from the first value and
continuing as long as any of those elements has a value.
For example, the format "%{[]family,familylang{%{family} (%{familylang})\n}}"
will expand the pattern "%{family} (%{familylang})\n" with a pattern
having only the first value of the family and familylang elemtns, then expands
it with the second values, then the third, etc.

</para><para>

As a special case, if an enumerate tag has only one element, and that element
has only one value in the pattern, and that value is of type FcLangSet, the
individual languages in the language set are enumerated.

</para><para>

A <firstterm>builtin</firstterm> tag
is one starting with the character "=" followed by a builtin
name.  The following builtins are defined:

<variablelist>

<varlistentry><term>
unparse
</term><listitem><para>
Expands to the result of calling FcNameUnparse() on the pattern.
</para></listitem></varlistentry>

<varlistentry><term>
fcmatch
</term><listitem><para>
Expands to the output of the default output format of the fc-match
command on the pattern, without the final newline.
</para></listitem></varlistentry>

<varlistentry><term>
fclist
</term><listitem><para>
Expands to the output of the default output format of the fc-list
command on the pattern, without the final newline.
</para></listitem></varlistentry>

<varlistentry><term>
pkgkit
</term><listitem><para>
Expands to the list of PackageKit font() tags for the pattern.
Currently this includes tags for each family name, and each language
from the pattern, enumerated and sanitized into a set of tags terminated
by newline.  Package management systems can use these tags to tag their
packages accordingly.
</para></listitem></varlistentry>

</variablelist>

For example, the format "%{+family,style{%{=unparse}}}\n" will expand
to an unparsed name containing only the family and style element values
from <parameter>pattern</parameter>.

</para><para>

The contents of any tag can be followed by a set of zero or more
<firstterm>converter</firstterm>s.  A converter is specified by the
character "|" followed by the converter name and arguments.  The
following converters are defined:

<variablelist>

<varlistentry><term>
basename
</term><listitem><para>
Replaces text with the results of calling FcStrBasename() on it.
</para></listitem></varlistentry>

<varlistentry><term>
dirname
</term><listitem><para>
Replaces text with the results of calling FcStrDirname() on it.
</para></listitem></varlistentry>

<varlistentry><term>
downcase
</term><listitem><para>
Replaces text with the results of calling FcStrDowncase() on it.
</para></listitem></varlistentry>

<varlistentry><term>
shescape
</term><listitem><para>
Escapes text for one level of shell expansion.
(Escapes single-quotes, also encloses text in single-quotes.)
</para></listitem></varlistentry>

<varlistentry><term>
cescape
</term><listitem><para>
Escapes text such that it can be used as part of a C string literal.
(Escapes backslash and double-quotes.)
</para></listitem></varlistentry>

<varlistentry><term>
xmlescape
</term><listitem><para>
Escapes text such that it can be used in XML and HTML.
(Escapes less-than, greater-than, and ampersand.)
</para></listitem></varlistentry>

<varlistentry><term>
delete(<parameter>chars</parameter>)
</term><listitem><para>
Deletes all occurrences of each of the characters in <parameter>chars</parameter>
from the text.
FIXME: This converter is not UTF-8 aware yet.
</para></listitem></varlistentry>

<varlistentry><term>
escape(<parameter>chars</parameter>)
</term><listitem><para>
Escapes all occurrences of each of the characters in <parameter>chars</parameter>
by prepending it by the first character in <parameter>chars</parameter>.
FIXME: This converter is not UTF-8 aware yet.
</para></listitem></varlistentry>

<varlistentry><term>
translate(<parameter>from</parameter>,<parameter>to</parameter>)
</term><listitem><para>
Translates all occurrences of each of the characters in <parameter>from</parameter>
by replacing them with their corresponding character in <parameter>to</parameter>.
If <parameter>to</parameter> has fewer characters than
<parameter>from</parameter>, it will be extended by repeating its last
character.
FIXME: This converter is not UTF-8 aware yet.
</para></listitem></varlistentry>

</variablelist>

For example, the format "%{family|downcase|delete( )}\n" will expand
to the values of the family element in <parameter>pattern</parameter>,
lower-cased and with spaces removed.

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