<pre class='metadata'>

Title: CSS Fonts Module Level 4

Shortname: css-fonts

Level: 4

Status: ED

Prepare for TR: no

Work Status: Revising

Group: CSSWG

ED: https://drafts.csswg.org/css-fonts-4/

TR: https://www.w3.org/TR/css-fonts-4/

Previous Version: https://www.w3.org/TR/2024/WD-css-fonts-4-20240201/

Former Editor: John Daggett, Invited Expert, https://twitter.com/nattokirai, w3cid 41498

Former Editor: Myles C. Maxfield, Formerly of Apple Inc., [email protected], w3cid 77180

Editor: Chris Lilley, W3C, http://svgees.us, w3cid 1438

Abstract: This specification defines modifications to the existing <a href="https://drafts.csswg.org/css-fonts-3/">CSS Fonts 3</a> specification along with additional features for font feature control, font variations, and chromatic (color) fonts.

At Risk: Synthesis of the 'font-variant-position' property

At Risk: The 'font-language-override!!property' property

At Risk: The 'font-language-override!!descriptor' descriptor

Ignored Terms: <named-palette-color>, cssText

Ignored Vars: res

Complain About: missing-example-ids true

Default Highlight: css

WPT Path Prefix: css/css-fonts/

WPT Display: closed

</pre>

<pre class="link-defaults">

spec:css-color-4; type:property; text:color

spec:css-color-5; type:type; text:<color>

spec:css-values; type:value; text:ex

spec:css22; type:value; for:/; text:block

spec:html; type:element; text:font

spec:fetch; type:dfn; for:/;

text:fetch

text:request

</pre>

<pre class=biblio>

{

"GRAPHITE": {

"href": "https://graphite.sil.org/graphite_techAbout.html",

"title": "Graphite technical overview",

"publisher": "SIL",

"date": "2012"

},

"PFE-report": {

"href": "https://www.w3.org/TR/PFE-evaluation/",

"authors": [

"Chris Lilley"

],

"status": "Note",

"publisher": "W3C",

"title": "Progressive Font Enrichment: Evaluation Report",

"date": "15 October 2020"

}

}

</pre>

<style>

/* work-around for https://github.com/tabatkins/bikeshed/issues/1799 */

div.example {

overflow: visible;

}

div.example>a.self-link::before {

content: "¶";

}

</style>

<h2 id="introduction">

Introduction</h2>

This specification includes and expands on

the basic font features described in the CSS3 Fonts specification ([[CSS-FONTS-3]]).

<!--

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-->

<h3 id="values">

Value Definitions</h3>

This specification follows the <a href="https://www.w3.org/TR/CSS2/about.html#property-defs">CSS property definition conventions</a> from [[!CSS2]]

using the <a href="https://www.w3.org/TR/css-values-3/#value-defs">value definition syntax</a> from [[!CSS-VALUES-3]].

Value types not defined in this specification are defined in CSS Values &amp; Units [[!CSS-VALUES-3]].

Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions,

all properties defined in this specification

also accept the <a>CSS-wide keywords</a> as their property value.

For readability they have not been repeated explicitly.

<h2 id="basic-font-props">

Basic Font Properties</h2>

The particular font face used to render a character is determined by

the font family and other font properties that apply to a given element.

This structure allows settings to be varied independently of each

other.

<!--

████████ ███████ ██ ██ ████████ ████████ ███ ██ ██ ████ ██ ██ ██

██ ██ ██ ███ ██ ██ ██ ██ ██ ███ ███ ██ ██ ██ ██

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██ ███████ ██ ██ ██ ██ ██ ██ ██ ██ ████ ████████ ██

-->

<h3 id="font-family-prop">

Font family: the 'font-family!!property' property</h3>

<pre class="propdef">

Name: font-family

Value: [ <<family-name>> | <<generic-family>> ]#

Initial: depends on user agent

Applies to: all elements and text

Inherited: yes

Percentages: n/a

Computed value: list, each item a string and/or <<generic-family>> keywords

Animation type: discrete

</pre>

<wpt>

font-family-name-000.xht

font-family-name-001.xht

font-family-name-002.xht

font-family-name-003.xht

font-family-name-004.xht

font-family-name-005.xht

font-family-name-006.xht

font-family-name-007.xht

font-family-name-008.xht

font-family-name-009.xht

font-family-name-010.xht

font-family-name-011.xht

font-family-name-012.xht

font-family-name-013.xht

font-family-name-014.xht

font-family-name-015.xht

font-family-name-016.xht

font-family-name-017.xht

font-family-name-018.xht

font-family-name-019.xht

font-family-name-020.xht

font-family-name-021.xht

font-family-name-022.xht

font-family-name-023.xht

font-family-name-024.xht

font-family-name-025.html

generic-family-keywords-003.html

standard-font-family-10.html

standard-font-family-11.html

standard-font-family-12.html

standard-font-family-13.html

standard-font-family-14.html

standard-font-family-15.html

standard-font-family-16.html

standard-font-family-17.html

standard-font-family-18.html

standard-font-family-19.html

standard-font-family-2.html

standard-font-family-20.html

standard-font-family-3.html

standard-font-family-4.html

standard-font-family-5.html

standard-font-family-6.html

standard-font-family-7.html

standard-font-family-8.html

standard-font-family-9.html

standard-font-family.html

test_font_family_parsing.html

animations/system-fonts.html

parsing/font-family-computed.html

parsing/font-family-invalid.html

parsing/font-family-valid.html

</wpt>

This property specifies a prioritized list of font family names or generic family names.

A font family defines a set of faces that vary in weight, width or slope.

CSS uses the combination of a family name with other font properties to select an individual face.

Using this selection mechanism,

rather than selecting a face via the style name as is often done in design applications,

allows some degree of regularity in textual display when fallback occurs.

Component values are a comma-separated list indicating alternatives.

A user agent iterates through the list of family names

until it matches an available font

that contains a glyph for the character to be rendered.

(See [[#cluster-matching]].)

This allows for differences in available fonts across platforms and

for differences in the range of characters supported by individual fonts.

<div class="example" id="ex-font-list">

<pre>

body {

font-family: Helvetica, Verdana, sans-serif;

}

</pre>

If Helvetica is available, it will be used when rendering.

If neither Helvetica nor Verdana is present,

then the generic font-family ''sans-serif'' font will be used.

</div>

There are three types of font family names, two of which may be used with this property:

<dl>

<dt><dfn id="family-name-value"><<family-name>></dfn>

<dd>

The name of a font family, such as Helvetica or Verdana in the previous example.

This might be a locally-instaled font, or might be a web font.

<dt><<generic-family>>

<dd>

Each <<generic-family>> keyword represents

a generic font choice,

and behaves as a potential alias for one or more locally-installed fonts

belonging to the specified generic font category.

A <<generic-family>> can thus be used as a fallback

for when an author's more specific font choices are not available.

There are three types of generic family:

1. Generics which apply to all Unicode characters

and will <em>always</em> match a locally installed font.

For example, ''monospaced''.

2. Generics which apply to all Unicode characters

but may not match to a locally installed font

on some systems.

For example, ''ui-rounded''.

3. Generics which are writing-system specific,

only apply to a subset of Unicode characters,

and may not match to a locally installed font

on some systems.

For example, ''generic(fangsong)''.

Authors are encouraged to append a generic font family as a last alternative

for improved robustness,

and to use a more specific generic font family, if applicable,

to prefer a specific style even if the individual named font family is not available.

Note that <<generic-family>> keywords cannot be quoted

(otherwise they are interpreted as a <<family-name>>).

The set of generic family keywords is defined in [[#generic-font-families]].

<dt><dfn id="system-family-name-value"><<system-family-name>></dfn>

<dd>

A locally installed system font, whose use is subject to certain constraints.

In particular, it may not be used with the ''font-family'' property,

but can be used with the ''font'' shorthand.

The following values refer to system fonts:

<dl dfn-type=value dfn-for=font>

<dt><dfn>caption</dfn>

<dd>The font used for captioned controls (e.g., buttons, drop-downs, etc.).

<dt><dfn>icon</dfn>

<dd>The font used to label icons.

<dt><dfn>menu</dfn>

<dd>The font used in menus (e.g., dropdown menus and menu lists).

<dt><dfn>message-box</dfn>

<dd>The font used in dialog boxes.

<dt><dfn>small-caption</dfn>

<dd>The font used for labeling small controls.

<dt><dfn>status-bar</dfn>

<dd>The font used in window status bars.

</dl>

<wpt>

system-fonts-serialization.tentative.html

</wpt>

</dd>

</dl>

<h4 id="family-name-syntax">

Syntax of <<family-name>>

</h4>

<pre class=prod><l><<family-name>></l> = <<string>> | <<custom-ident>>+</pre>

Font family names other than generic families or system font families

must either be given quoted as <<string>>s,

or unquoted as a sequence of one or more <<custom-ident>>.

Note: This means most punctuation characters and digits at the start of

each token must be escaped in unquoted font family names.

<div class="example invalid" id="ex-no-unquoted-punctuation">

To illustrate this, the following declarations are invalid:

<pre>

font-family: Red/Black, sans-serif;

font-family: "Lucida" Grande, sans-serif;

font-family: Ahem!, sans-serif;

font-family: test@foo, sans-serif;

font-family: #POUND, sans-serif;

font-family: Hawaii 5-0, sans-serif;

</pre>

</div>

Any identifier

which could be misinterpreted

as a pre-defined keyword in the font-family value definition,

or the [=CSS-wide keywords=],

is not allowed.

Note: this means that if you really have a font

whose name

is the same as one of the <<generic-family>> names,

or the system font names,

or the [=CSS-wide keywords=],

it <em>must</em> be quoted.

<div class="example" id="ex-valid-unusual-generic-like">

To illustrate this,

the following unusual font family names are valid

because they are quoted:

<pre>

font-family: "sans-serif", sans-serif;

font-family: "default", sans-serif;

font-family: "initial", sans-serif;

font-family: "inherit", sans-serif;

</pre>

</div>

If a sequence of identifiers is given as a <<family-name>>,

the computed value is the name

converted to a string

by joining all the identifiers in the sequence by single spaces.

To avoid mistakes in escaping,

it is recommended to quote font family names

that contain white space, digits,

or punctuation characters other than hyphens:

<div class="example" id="ex-best-quote">

Quoting font families prevents escaping mistakes.

<pre>

body { font-family: "New Century Schoolbook", serif }

&lt;body style="font-family: '21st Century', fantasy">

</pre>

</div>

Font family <em>names</em> that happen to be the same as

a 'font-family!!property' keyword value

(e.g. <a>CSS-wide keywords</a> such as ''inherit'', or

<<generic-family>> keywords such as ''serif'')

must be quoted to prevent confusion

with the keywords of the same names.

UAs must not consider these keywords as matching the <<family-name>> type.

<h4 id="generic-family-name-syntax">

Syntax of <<generic-family>>

</h4>

<!-- <pre class=prod>

<dfn><<generic-family>></dfn> = generic(<<generic-script-specific>>) | <<generic-complete>> | <<generic-incomplete>>

<dfn><<generic-script-specific>></dfn> = <a href="">kai</a> | fangsong | nastaliq

<dfn><<generic-complete>></dfn> = serif | sans-serif | system-ui | cursive | fantasy | math | monospace

<dfn><<generic-incomplete>></dfn> = ui-serif | ui-sans-serif | ui-monospace | ui-rounded

</pre> -->

<pre class=prod>

<dfn><<generic-family>></dfn> = <<generic-script-specific>>| <<generic-complete>> | <<generic-incomplete>>

<dfn><<generic-script-specific>></dfn> = <l>''font-family/generic(fangsong)''</l> | <l>''font-family/generic(kai)''</l> | <l>''font-family/generic(khmer-mul)''</l> | <l>''font-family/generic(nastaliq)''</l>

<dfn><<generic-complete>></dfn> = <l>''font-family/serif''</l> | <l>''font-family/sans-serif''</l> | <l>''font-family/system-ui''</l> | <l>''font-family/cursive''</l> | <l>''font-family/fantasy''</l> | <l>''font-family/math''</l> | <l>''font-family/monospace''</l>

<dfn><<generic-incomplete>></dfn> = <l>''font-family/ui-serif''</l> | <l>''font-family/ui-sans-serif''</l> | <l>''font-family/ui-monospace''</l> | <l>''font-family/ui-rounded''</l>

</pre>

To make the syntax less succeptible to clashes, more recently defined generic font families are identified using a functional syntax.

<div class="example" id="ex-generic-functional">

<pre>

body { font-family: "Adobe Fangsong Std R", generic(fangsong), serif}

</pre>

The first choice in this example is a specific, named font, in Fang Song (仿宋) style.

The family name is enclosed in quotes as it contains space characters.

The second is a recently added script-specific generic font; it is unicode-range specific

and so may not match to an actual installed font on some systems;

but if it exists it will be an example of the requested style.

The third is a universal generic font, which is guaranteed to match on all systems.

</div>

<h4 id="system">

Syntax of <<system-family-name>>

</h4>

<pre class="prod">

<l><<system-family-name>></l> = <l>''caption''</l> | <l>''icon''</l> | <l>''menu''</l> | <l>''message-box''</l> | <l>''small-caption''</l> | <l>''status-bar''</l>

</pre>

<h4 id="font-families">

Relationship Between Faces and Families

</h4>

A font family name only specifies a name given to a set of font faces;

it does not specify an individual face.

<div class="example" id="ex-futura-matches">

For example, given the availability of the fonts below,

Futura would match but Futura Medium would not:

<figure>

<img alt="family and face names" src="images/familyvsfacename.png" width="597" height="151">

<figcaption>Family and individual face names</figcaption>

</figure>

</div>

Note: The CSS definition of font attributes used for selection

are explicitly not intended to define a font taxonomy.

A type designer's idea of a family can often extend

to a set of faces that vary along axes other than just

the standard axes of

weight ('font-weight!!property'),

width ('font-width!!property'),

and slant ('font-style!!property').

A family can vary along axes that are unique to that family.

The CSS font selection mechanism merely

provides a way to determine the “closest” match

when substitution is necessary.

Note: The precise way a set of fonts are grouped into font families

varies depending upon the platform font management APIs.

For example, the Windows GDI API only allows four faces to be grouped into a family,

while the DirectWrite API,

Core Text API,

and other platforms support

font families with a variety of weights, widths, and slopes

(see [[#platform-props-to-css]] for more details).

See [[#localized-name-matching]] below for information on how

font-family names are matched.

<h4 id="generic-font-families">

Generic font families</h4>

A generic font family is a font family which has a standard name (as defined by CSS), but which is an alias for an existing installed font family present on the system.

However, a single generic font family may be a [=composite face=]

combining different typefaces based on such things as

the Unicode range of the character,

the <a>content language</a> of the containing element,

user preferences, system settings, etc.

Different generic font families may map to the same used font.

<wpt>

generic-family-keywords-001.html

generic-family-keywords-002.html

</wpt>

Note: Generic font families are intended to be widely implemented on many platforms, unlike arbitrary <<family-name>>s which are usually platform-specific names. They are expected to map to different fonts on different platforms. Authors may specify these generic family names if they desire their text to follow a particular design on many platforms, and are not particular about which specific font is chosen on those platforms.

User agents should provide reasonable default choices for the generic font families,

that express the characteristics of each family as well as possible,

within the limits allowed by the underlying technology.

User agents are encouraged to allow users to select alternative faces for the generic font families.

<dl dfn-for="font-family,<generic-family>" dfn-type=value>

<dt id="serif-def"><dfn>serif</dfn>

<dd>

Serif fonts represent

glyphs that have finishing strokes,

flared or tapering ends,

or have actual serifed endings (including slab serifs).

Serif fonts are typically proportionately-spaced.

They often display a greater variation between thick and thin strokes

than fonts from the ''sans-serif'' generic font family.

Note: ''serif'' and ''sans-serif''

only apply to a small handful of writing scripts.

Their use as generic font families in CSS is historical,

and reflects the Latin-centric nature

of early Web development.

Better and more widely applicable names would have been,

for example, "modulated" and "monoline".

However, for reasons of Web compatibility,

these names cannot be changed.

CSS uses the term "serif" to apply to a font for any script,

although other names might be more familiar for particular scripts,

such as Mincho (Japanese),

Sung or Song (Chinese),

Batang (Korean).

For Arabic, the Naskh style would correspond to ''serif''.

''serif'' must always map to at least one matched font face.

Note: No guarantee is placed on the character coverage of that font

face. Therefore, the font ''serif'' is mapped to may not end up being

used for all content.

<figure>

<img alt="sample serif fonts" src="images/serifexamples.png" width="586" height="110">

<figcaption>Sample serif fonts</figcaption>

</figure>

<dt id="sans-serif-def"><dfn>sans-serif</dfn>

<dd>

Glyphs in sans-serif fonts,

as the term is used in CSS,

are generally low contrast

(vertical and horizontal stems have the close to the same thickness)

and have stroke endings that are plain

(without any flaring, cross stroke, or other ornamentation).

Sans-serif fonts are typically proportionately-spaced.

They often have little variation between thick and thin strokes,

compared to fonts from the ''serif'' family.

CSS uses the term "sans-serif" to apply to a font for any script,

although other names might be more familiar for particular scripts,

such as Gothic (Japanese),

Hei (Chinese),

or Gulim (Korean).

''sans-serif'' must always map to at least one matched font face.

Note: No guarantee is placed on the character coverage of that font

face. Therefore, the font ''sans-serif'' is mapped to may not end up being

used for all content.

<figure>

<img alt="sample sans-serif fonts" src="images/sansserifexamples.png" width="621" height="117">

<figcaption>Sample sans-serif fonts</figcaption>

</figure>

<dt id="cursive-def"><dfn>cursive</dfn>

<dd>

Glyphs in cursive fonts generally use a script style,

and the result looks more like handwritten pen or brush writing than printed letterwork.

CSS uses the term "cursive" to apply to a font for any script,

although other names such as Chancery, Brush, Swing and Script are also used in font names.

<figure>

<img alt="sample cursive fonts" src="images/cursiveexamples.png" width="493" height="150">

<figcaption>Sample cursive fonts</figcaption>

</figure>

<dt id="fantasy-def"><dfn>fantasy</dfn>

<dd>

Fantasy fonts are primarily decorative or expressive fonts

that contain decorative or expressive representations of characters.

These do not include Pi or Picture fonts which do not represent actual characters.

<figure>

<img alt="sample fantasy fonts" src="images/fantasyexamples.png" width="763" height="114">

<figcaption>Sample fantasy fonts</figcaption>

</figure>

<dt id="monospace-def"><dfn>monospace</dfn>

<dd>

The sole criterion of a monospace font is that all glyphs have the same fixed width.

This is often used to render samples of computer code.

''monospace'' must always map to at least one matched font face.

Note: No guarantee is placed on the character coverage of that font

face. Therefore, the font ''monospace'' is mapped to may not end up being

used for all content.

<figure>

<img alt="sample monospace fonts" src="images/monospaceexamples.png" width="608" height="102">

<figcaption>Sample monospace fonts</figcaption>

</figure>

<dt id="system-ui-def"><dfn>system-ui</dfn>

<dd>

This generic font family lets text render with the default user interface font

(which, as with all [[#generic-font-families]], may be a composite font)

on the platform on which the UA is running.

A cross-platform UA should use different fonts on its different supported platforms.

The purpose of ''system-ui'' is to allow web content

to integrate with the look and feel of the native OS.

This is useful for hybrid, web or cross-platform applications.

<wpt>

system-ui-ar.html

system-ui-ja-vs-zh.html

system-ui-ja.html

system-ui-mixed.html

system-ui-ur-vs-ar.html

system-ui-ur.html

system-ui-zh.html

system-ui.html

</wpt>

The precise font(s) used will depend on factors such as

platform support, platform language, locale settings,

user preferences, Unicode coverage and the content language.

UA may optionally choose to use the text rendering engine provided by the platform when using

''system-ui'' to match the appearance of the default user interface more closely.

<div class="example" id="ex-system-ui-opaque">

As with other generic font families,

the substitution of specific installed fonts for ''system-ui''

does not affect the computed style.

<pre>

&lt;div id="system-text" style="font-family: system-ui"&gt;&lt;/div&gt;

...

window.getComputedStyle(document.getElementById("system-text")).getPropertyValue("font-family");

</pre>

The script above should not have any knowledge of how ''system-ui''

is expanded to include a collection of system user interface fonts.

In particular, the above script should yield a result of "system-ui" on every platform.

</div>

Note: ''system-ui'' is highly dependent on the platform environment as multiple factors may

affect the default user interface font, and may have verying level of text rendering support.

This may cause the displayed typeface to be undesirable for some end users

(e.g. Simplified Chinese users might get a monospaced serif font on older version of Windows;

''lang'' attribute might not affect displayed font in cases like ''lang="uk"'' in Russian locale

or ''lang="ja"'' in Chinese locale).

Some operating system vendors does not offer means to customise ''system-ui'',

unlike UAs that generally allow users to customise the generic ''sans-serif'' or ''serif'' font family.

As the name implies, ''system-ui'' is intended for use with UI elements in web application, and not for large paragraphs of text or articles.

<dt id="math-def"><dfn>math</dfn>

<dd>

This font family is intended for use with mathematical expressions.

<!-- largely from https://docs.microsoft.com/en-us/typography/opentype/spec/math -->

Such fonts may include additional data

(for example, the OpenType MATH table)

to help with the hierarchical process of equation layout.

In particular, they may contain

stylistic and stretching glyph variants

useful in setting mathematical equations.

<dt id="generic(fangsong)-def"><dfn>generic(fangsong)</dfn>

<dd>

This font family is used for Fang Song (仿宋) typefaces in Chinese.

Fang Song is a relaxed, intermediate form

between Song (''serif'') and Kai (''generic(kai)'').

Typically, the horizontal lines are tilted,

the endpoint flourishes are smaller,

and there is less variation in stroke width,

compared to a Song style.

Fang Song is often used for official Chinese Government documents.

Note: ''generic(fangsong)'' might not map to any locally installed font,

but if it does, that font will be in Fang Song style.

<figure>

<img style="width:75vw" alt="" src="images/fangsong.svg" width="800" height="380">

<figcaption>Chinese text displayed with sample fang song fonts</figcaption>

</figure>

<dt id="generic(kai)-def"><dfn>generic(kai)</dfn>

<dd>

This font family is used in

Simplified &amp; Traditional Chinese.

A major typeface, which provides calligraphic styles for Chinese text.

It shows notable handwriting features.

Kai is commonly used in official documents and textbooks.

Most official documents in Taiwan use Kai in full text.

Kai can also be combined with other typefaces

to be used in text that needs to be differentiated

from the rest of the content,

for example, headlines, references, quotations, and dialogs.

Note: ''generic(kai)'' might not map to any locally installed font,

but if it does, that font will be in Kai style.

<figure>

<img style="width:75vw" alt="" src="images/kaiti.svg" width="800" height="380">

<figcaption>Chinese text displayed with sample kai fonts</figcaption>

</figure>

</dd>

<dt id="generic(khmer-mul)-def"><dfn>generic(khmer-mul)</dfn>

<dd>

This font family is used in

the Khmer language (used in Cambodia),

for titles and headings,

or to emphasise important names or nouns.

Compared to the upright (âksâr chôr) style,

which is used for regular text,

âksâr mul is characterized by

heavier, more rounded letter shapes,

and may include more ligated forms.

Despite the visually heavier style,

the font weight for regular text in

''generic(khmer-mul)'' is unchanged (400).

Note: ''generic(khmer-mul)'' might not map to

any locally installed font,

but if it does, that font will be in âksâr mul style.

<figure>

<img style="width:30vw" alt="" src="images/vi-tu-comparison.png" width="512" height="625">

<figcaption>Cambodian text displayed in:

(top) âksâr chôr style, set in Khmer OS Battambang;

(center) âksâr mul style, set in Khmer OS Moul v6, with no ligatures;

(bottom) âksâr mul style, set in Khmer OS Moul v4, with two ligatures. All fonts by Dan Hong.

</figcaption>

</figure>

</dd>

<dt id="generic(nastaliq)-def"><dfn>generic(nastaliq)</dfn>

<dd>

This font family is the standard way of writing Urdu and Kashmiri,

and is also often a preferred style for Persian and other language text,

especially in literary genres such as poetry.

Key features include a sloping baseline for joined letters,

and overall complex shaping and positioning for base letters and diacritics alike.

There are also distinctive shapes for many glyphs and ligatures.

It is important not to fall back to a naskh style

for languages such as Urdu and Kashmiri.

Note: ''generic(nastaliq)'' might not map to any locally installed font,

but if it does, that font will be in Nastaliq style.

<figure>

<img style="width:25vw" alt="السلام علیکم" src="images/urdu-nastaliq.svg" width="600" height="346">

<figcaption>Urdu text displayed with a sample nastaliq font (Noto Nastaliq Urdu)</figcaption>

</figure>

<figure>

<img style="width:25vw" alt="السلام علیکم" src="images/urdu-naskh.svg" width="600" height="346">

<figcaption>Urdu text displayed with a fallback naskh font (Scheherazade New)</figcaption>

</figure>

<dt id="ui-serif-def"><dfn>ui-serif</dfn>

<dd>

This font family is used for the serif variant of the system's

user interface. The purpose of ''ui-serif'' is to allow web

content to integrate with the look and feel of the native OS.

Note: ''ui-serif'' is not expected to map to any font on platforms

without an appropriate system font.

Note: see notes on ''system-ui'' for potential issues.

<div class="example" id="ex-sample-ui-serif">

<figure>

<img alt="sample ui-serif font" src="images/ui-serif.png" width="743" height="185">

<figcaption>Sample ui-serif font on macOS Catalina and iOS 13: New York</figcaption>

</figure>

</div>

<dt id="ui-sans-serif-def"><dfn>ui-sans-serif</dfn>

<dd>

This font family is used for the sans-serif variant of the system's

user interface. The purpose of ''ui-sans-serif'' is to allow web

content to integrate with the look and feel of the native OS.

Note: ''ui-sans-serif'' is not expected to map to any font on platforms

without an appropriate system font.

Note: see notes on ''system-ui'' for potential issues.

<div class="example" id="ex-sample-ui-sans">

<figure>

<img alt="sample ui-sans-serif font" src="images/ui-sans-serif.png" width="743" height="149">

<figcaption>Sample ui-sans-serif font on macOS Catalina and iOS 13: San Francisco</figcaption>

</figure>

</div>

<dt id="ui-monospace-def"><dfn>ui-monospace</dfn>

<dd>

This font family is used for the monospaced variant of the

system's user interface. The purpose of ''ui-monospace'' is to

allow web content to integrate with the look and feel of the

native OS.

Note: ''ui-monospace'' is not expected to map to any font on platforms

without an appropriate system font.

Note: see notes on ''system-ui'' for potential issues.

<div class="example" id="ex-sample-ui-mono">

<figure>

<img alt="sample ui-monospace font" src="images/ui-monospace.png" width="743" height="145">

<figcaption>Sample ui-monospace font on macOS Catalina and iOS 13: SF Mono</figcaption>

</figure>

</div>

<dt id="ui-rounded-def"><dfn>ui-rounded</dfn>

<dd>

This font family is used for the rounded variant of the system's

user interface. The purpose of ''ui-rounded'' is to allow web

content to integrate with the look and feel of the native OS.

Note: ''ui-rounded'' is not expected to map to any font on platforms

without an appropriate system font.

Note: see notes on ''system-ui'' for potential issues.

<div class="example" id="ex-sample-ui-rounded">

<figure>

<img alt="sample ui-rounded font" src="images/ui-rounded.png" width="743" height="180">

<figcaption>Sample ui-rounded font on macOS Catalina and iOS 13: SF Rounded</figcaption>

</figure>

</div>

</dl>

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<h3 id="font-weight-prop">Font weight: the 'font-weight!!property' property</h3>

<pre class="propdef">

Name: font-weight

Value: <<font-weight-absolute>> | bolder | lighter

Initial: normal

Applies to: all elements and text

Inherited: yes

Percentages: n/a

Computed value: a number, see below

Animation type: by computed value type

</pre>

<wpt>

font-weight-bolder-001.xht

font-weight-lighter-001.xht

font-weight-normal-001.xht

font-weight-sign-function.html

test-synthetic-bold.html

synthetic-bold-space-width.html

animations/font-weight-composition.html

parsing/font-weight-computed.html

parsing/font-weight-invalid.html

parsing/font-weight-valid.html

variations/font-parse-numeric-stretch-style-weight.html

variations/font-weight-interpolation.html

variations/font-weight-lighter-bolder.html

variations/font-weight-matching-installed-fonts.html

variations/font-weight-matching.html

variations/font-weight-metrics.html

variations/font-weight-parsing.html

</wpt>

The 'font-weight!!property' property specifies the weight of glyphs in the font,

their degree of blackness, or stroke thickness.

This property accepts values of the following:

<pre class="prod"><dfn id="font-weight-absolute-values">&lt;font-weight-absolute&gt;</dfn> = [ normal | bold | <<number [1,1000]>> ]</pre>

Values have the following meanings:

<dl dfn-for=font-weight dfn-type=value>

<dt id="font-weight-numeric-values"><dfn><<number [1,1000]>></dfn>

<dd>

Each number indicates a weight that is at least as dark as its predecessor.

Only values greater than or equal to 1, and less than or equal to 1000, are valid,

and all other values are <a>invalid</a>.

Numeric values typically correspond to the commonly used weight names below.

<ul>

<li>100 - Thin

<li>200 - Extra Light (Ultra Light)

<li>300 - Light

<li>400 - Normal

<li>500 - Medium

<li>600 - Semi Bold (Demi Bold)

<li>700 - Bold

<li>800 - Extra Bold (Ultra Bold)

<li>900 - Black (Heavy)

</ul>

Note: A font might internally provide its own weight name mappings,

but those mappings within the font are disregarded in CSS.

<dt><dfn>normal</dfn>

<dd>

Same as ''400''.

<dt><dfn>bold</dfn>

<dd>

Same as ''700''.

<dt><dfn>bolder</dfn>

<dd>

Specifies a bolder weight than the inherited value.

See [[#relative-weights]].

<dt><dfn>lighter</dfn>

<dd>

Specifies a lighter weight than the inherited value.

See [[#relative-weights]].

</dl>

Font formats that use a scale other than a nine-step scale

should map their scale onto the CSS scale

so that 400 roughly corresponds with a face that would be labeled as Regular, Book, Roman

and 700 roughly matches a face that would be labeled as Bold.

Alternately, weights may be inferred from style names

that correspond roughly with the scale above.

The scale is relative,

so a face with a larger weight value must never appear lighter.

If style names are used to infer weights,

care should be taken to handle variations in style names across locales.

<h4 id="relative-weights">

Relative Weights</h4>

Specified values of ''bolder'' and ''lighter'' indicate weights

relative to the weight of the parent element.

The computed weight is calculated based on the inherited 'font-weight!!property' value

using the chart below.

<table id="bolderlighter" class="data">

<thead>

<tr>

<th>Inherited value (<var>w</var>)

<th>bolder

<th>lighter

<tbody>

<tr><th><var>w</var> &lt; 100<td>400<td>No change

<tr><th>100 &le; <var>w</var> &lt; 350<td>400<td>100

<tr><th>350 &le; <var>w</var> &lt; 550<td>700<td>100

<tr><th>550 &le; <var>w</var> &lt; 750<td>900<td>400

<tr><th>750 &le; <var>w</var> &lt; 900<td>900<td>700

<tr><th>900 &le; <var>w</var><td>No change<td>700

</table>

Note: The table above is equivalent to selecting the next relative bolder or lighter face,

given a font family containing normal and bold faces

along with a thin and a heavy face.

Authors who desire finer control over the exact weight values used for a given element

can use numerical values instead of relative weights.

<h4 id="missing-weights">

Missing weights</h4>

Quite often there are only a few weights available for a particular font family.

When a weight is specified for which no face exists, a face with a nearby weight is used.

In general, bold weights map to faces with heavier weights and light weights map to faces with lighter weights.

(See the [[#font-matching-algorithm]] for a precise definition.)

<div class="example" id="ex-nearby-weights">

The examples here illustrate which face is used for different weights.

Grey indicates that a face for the desired weight does not exist, so a face with a nearby weight is used.

<figure>

<img alt="weight mappings for a family with 400, 700 and 900 weights" src="images/optimaweights.png" width="697" height="127">

<figcaption>Weight mappings for a font family with 400, 700 and 900 weight faces</figcaption>

</figure>

<figure>

<img alt="weight mappings for a family with 300, 600 weights" src="images/hiraginoweights.png" width="692" height="123">

<figcaption>Weight mappings for a font family with 300 and 600 weight faces</figcaption>

</figure>

</div>

Most user agents model a font as having a particular weight

which often corresponds to one of the numbers in the nine-step scale

described <a href="#font-weight-numeric-values">above</a>.

While this is true of most fonts, some fonts might be configurable so as to support a range of weights.

In this situation, the user agent uses a face with a weight as close as possible to the weight requested

(see [[#font-matching-algorithm]] for the precise algorithm).

In particular, a user agent using a font which supports a range of weights

should behave the same as if a font is present at each individual weight in the range.

For TrueType / OpenType fonts that use variations,

the <code>wght</code> variation is used to implement varying weights.

Fractional weights are valid.

Although the practice is not well-loved by typographers,

bold faces are often synthesized by user agents for families that lack actual bold faces.

For the purposes of font matching,

these faces must be treated as if they exist within the family.

Authors can explicitly avoid this behavior by using the 'font-synthesis' property.

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<h3 id="font-width-prop">