CSS Fonts Module Level 5 W3C Working Draft , 11 August 2026 More details about this document This version: https://www.w3.org/TR/2026/WD-css-fonts-5-20260811/ Latest published version: https://www.w3.org/TR/css-fonts-5/ Editor's Draft: https://drafts.csswg.org/css-fonts-5/ Previous Versions: https://www.w3.org/TR/2021/WD-css-fonts-5-20211221/ https://www.w3.org/TR/2024/WD-css-fonts-4-20240201/ History: https://www.w3.org/standards/history/css-fonts-5/ Feedback: CSSWG Issues Repository Inline In Spec Editor: Chris Lilley ( W3C ) Former Editor: Myles C. Maxfield ( Formerly of Apple Inc. ) Suggest an Edit for this Spec: GitHub Editor Delta Spec: yes Test Suite: https://wpt.fyi/results/css/css-fonts/ Copyright © 2026 World Wide Web Consortium . W3C ® liability , trademark and permissive document license rules apply. Abstract This specification defines modifications to the existing CSS Fonts 4 specification along with additional features. CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc. Status of this document This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C standards and drafts index. This document was published by the CSS Working Group as a Working Draft using the Recommendation track . Publication as a Working Draft does not imply endorsement by W3C and its Members. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than a work in progress. Please send feedback by filing issues in GitHub (preferred), including the spec code “css-fonts” in the title, like this: “[css-fonts] …summary of comment… ”. All issues and comments are archived . 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Table of Contents 1 Introduction 1.1 Value Definitions 2 Text-Scale meta element 2.1 Keywords 2.2 The legacy keyword 2.3 The scale keyword 3 Basic Font Properties 3.1 Font family: the font-family property 3.1.1 Generic font families 3.2 Font weight: the font-weight property 3.3 Font style: the font-style property 3.4 Relative sizing: the font-size-adjust property 4 Font Resources 4.1 The @font-face rule 4.2 Font reference: the src descriptor 4.2.1 Parsing the src descriptor 4.3 Font property descriptors: the font-size 4.4 Glyph Size Multiplier: the size-adjust descriptor 4.5 Line Height Font Metrics Overrides: the ascent-override , descent-override , and line-gap-override descriptors 4.6 Superscript and subscript metrics overrides: the superscript-position-override , subscript-position-override , superscript-size-override and subscript-size-override descriptors 5 Font Feature Properties 5.1 Font language override: the font-language-override property 6 Font Feature and Variation Resolution 7 Font Variation Properties 7.1 Optical sizing control: the font-optical-sizing property 8 Font Technologies and Formats 8.1 Font tech 9 Object Model 9.1 The CSSFontFaceRule interface 10 Security Considerations 11 Privacy Considerations 12 Acknowledgments 13 Changes 13.1 Changes since the WD of 6 February 2024 13.2 Changes since the WD of 21 December 2021 13.3 Changes since the WD of 2021-07-29 13.4 Changes since the FPWD of 2021-06-29 Conformance Document conventions Conformance classes Partial implementations Implementations of Unstable and Proprietary Features Non-experimental implementations Index Terms defined by this specification Terms defined by reference References Normative References Non-Normative References Property Index @font-face Descriptors IDL Index Issues Index 1. Introduction The CSS Fonts Level 4 specification ( [CSS-FONTS-4] ) describes the controls CSS provides for selecting and using fonts within documents, including support for variable fonts and color fonts. The ideas here are additions or modifications to the properties and rules defined in CSS Fonts Level 4. This specification is currently a delta to the CSS Fonts Level 4 specification. Do not assume that if something is not here, it has been dropped. 1.1. Value Definitions This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3] . Value types not defined in this specification are defined in CSS Values & 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 CSS-wide keywords as their property value. For readability they have not been repeated explicitly. 2. Text-Scale meta element User agents must calculate the computed value of medium by multiplying 16px by the text scale factor . User agents must also apply this factor when determining the computed sizes of the other <absolute-size> keywords. However, user agents should scale these other keywords non-linearly to preserve readability. Note: Applying a linear scale to all keywords would render large fonts excessively large. See the WCAG discussion on minimum and maximum critical font sizes . A document with a meta tag whose name attribute is an ASCII case-insensitive match for "text-scale" is recognized as controlling the text scale factor . The value of the content attribute must be an ASCII case-insensitive match for one of the recognized keywords. Otherwise the tag is ignored. Documents without this meta tag will have an assumed default value of legacy . < meta name = "text-scale" content = "scale" /> There must not be more than one meta element with its name attribute value set to an ASCII case-insensitive match for text-scale per document. 2.1. Keywords The recognized keywords in the text-scale meta element are: legacy The preferred-text-scale environment variable returns the user’s OS-level font factor on mobile devices, but 1 on desktop devices. text scale factor incorporates UA-level font preferences but OS-level font preferences are ignored. Note: Equivalent to omitting a text-scale meta tag or including an unrecognized content attribute keyword. scale The preferred-text-scale environment variable returns the user’s OS-level font preferences. text scale factor incorporates both UA-level and OS-level font preferences. 2.2. The legacy keyword When the value of the text-scale content attribute is legacy , the text scale factor is the font scale factor the user has chosen from any settings provided only by the user agent. The preferred-text-scale environment variable value must be 1 on desktop platforms. On mobile platforms: If the operating system provides a text scale setting AND the UA hasn’t already applied that factor to the medium font size, the preferred-text-scale environment variable returns the multiplier that the user has chosen in the operating system’s text scale setting. Note: At the time of publishing, all combinations of Android, iOS, Firefox, Safari, and Chrome satisfy this first condition. Otherwise the preferred-text-scale environment variable returns 1. 2.3. The scale keyword When the value of the text-scale content attribute is scale , the text scale factor matches the user’s preferred paragraph text size (as determined from a combination of OS and UA preferences) divided by 16px. The preferred-text-scale environment variable must return the text scale factor . Further, when the value of the text-scale content attribute is scale , the user agent should skip all font-sizing interventions it would otherwise perform in an attempt to automatically honor the user’s preferences. E.g. text autosizing on mobile (See CSS Size Adjustment 1 § 1 Introduction ) and full-application zoom ( popular browsers do this on Windows) . Note: Authors are expected to use <meta name= "text-scale" content= "scale" > in stylesheets so that the medium font size will reflect a combination of the user’s font preferences, whether those are specified at the OS level or the UA level. The author will then be able to use rem throughout the page to honor the user’s font preferences. If authors don’t alter the :root font size, content sized with rem units will be relative to the preferred text scale <!DOCTYPE html> < html > <!-- leave this element's font-size as the default --> < head > < meta name = "text-scale" content = "scale" /> </ head > < body > < div style = "font-size: 1rem;" > This font size obeys the user's font preferences, **whether those preferences are specified at the operating system level or the user agent level** </ div > < div style = "font-size: 20px;" > This font size does NOT respect the user's font preferences. < div style = "font-size: 1rem;" > But this font size does! </ div > </ div > </ body > </ html > 3. Basic Font Properties w3c/csswg-drafts/126 [css-fonts] Specifying changes to parameters for fallback fonts 3.1. Font family: the font-family property 3.1.1. Generic font families In addition to the CSS Fonts 4 § 2.1.5 Generic font families in CSS Fonts Level 4, the following new generic font families are also defined. w3c/csswg-drafts/4910 [meta] [css-fonts] Criteria for generic font families xxx Placeholder text for the xxx generic font family. w3c/csswg-drafts/4566 [css-fonts] Should we start a registry for additional generic fonts? 3.2. Font weight: the font-weight property w3c/csswg-drafts/2690 [css-fonts-4] Percentages in font-weight for relative weights 3.3. Font style: the font-style property w3c/csswg-drafts/4044 [css-fonts] Vertical text doesn't play nicely with font-style and font-stretch 3.4. Relative sizing: the font-size-adjust property Name: font-size-adjust Value: none | [ ex-height | cap-height | ch-width | ic-width | ic-height ] ? [ from-font | <number [0,∞]> ] Initial: none Applies to: all elements and text Inherited: yes Percentages: N/A Computed value: the keyword none , or a pair of a metric keyword and a <number> Canonical order: per grammar Animation type: discrete if the keywords differ, otherwise by computed value type For any given font size, the apparent size and effective legibility of text varies across fonts as a function of their design. For example, for bicameral scripts such as Latin or Cyrillic that distinguish between upper and lowercase letters, the relative height of lowercase letters compared to their uppercase counterparts is a determining factor of legibility. In situations where font fallback occurs, fallback fonts might not share the same ratios as the desired font family for key typographic metrics, and will thus appear to be a different size and possibly be less readable. Tests font-size-adjust-ic-height.html (live test) (source) w3c/csswg-drafts/8792 [css-fonts-5] font-size-adjust: ic-height The font-size-adjust property provides a way to preserve the readability and apparent size of text when font fallback occurs. It does this by adjusting the used font size so that the specified metric is the same regardless of the font used. Values have the following meanings: none No special font-size adjustment is applied. ex-height | cap-height | ch-width | ic-width | ic-height Specifies the font metric to normalize, defaulting to ex-height : ex-height Normalize the aspect value of the fonts, using the x-height divided by the font size. cap-height Normalize the cap-height of the fonts, using the cap-height by the font size. ch-width Normalize the horizontal narrow pitch of the fonts, using the advance width of “0” (ZERO, U+0030) divided by the font size. ic-width Normalize the horizontal wide pitch of the font, using the advance width of “水” (CJK water ideograph, U+6C34) divided by the font size. ic-height Normalize the vertical wide pitch of the font, using the advance height of “水” (CJK water ideograph, U+6C34) divided by the font size. w3c/csswg-drafts/6384 [css-fonts-5] font-size-adjust with missing metrics <number [0,∞]> Each font’s used size is normalized to match the chosen font metric to this specified proportion of the computed font-size . In other words, for each glyph, the adjusted font size to use u is calculated as: u = ( m / m′ ) s where: s = computed 'font-size!!property' value m = metric as specified by the 'font-size-adjust' property m′ = metric as specified in the actual font u = adjusted font-size to use Negative values are invalid. from-font Computes to the <number> corresponding to the specified metric of the first available font , if it exists. Otherwise, the same as none . Tests font-size-adjust-composition.html (live test) (source) font-size-adjust-interpolation.html (live test) (source) font-size-adjust-013.html (live test) (source) font-size-adjust-014.html (live test) (source) font-size-adjust-metrics-override.html (live test) (source) font-size-adjust-text-orientation.html (live test) (source) font-size-adjust-units-001.html (live test) (source) font-size-adjust-computed.html (live test) (source) font-size-adjust-invalid.html (live test) (source) font-size-adjust-valid.html (live test) (source) The style defined below defines Verdana as the desired font family, but if Verdana is not available Futura or Times will be used. One paragraph also has font-size-adjust specified. p { font-family : Verdana , Futura , Times ; } p.adj { font-size-adjust : 0.545 ; } <p>Lorem ipsum dolor sit amet , ...</p> <p class= "adj" >Lorem ipsum dolor sit amet , ...</p> Verdana has a relatively high aspect value of 0.545, meaning lowercase letters are relatively tall compared to uppercase letters, so at small sizes text appears legible. Times has a lower aspect value of 0.447, and so if fallback occurs, the text will be less legible at small sizes than Verdana unless font-size-adjust is also specified. Note: For text which uses diacritics, too large an x-height will actually decrease legibility as the diacritics become cramped. How text rendered in each of these fonts compares is shown below, the columns show text rendered in Verdana, Futura and Times. The same font-size value is used across cells within each row and red lines are included to show the differences in x-height. In the upper half, each row is rendered in the same font-size value. The same is true for the lower half, but in this half the font-size-adjust property is also set to 0.545, so that the actual font size is adjusted to preserve the x-height of Verdana across each row. Note how small text remains relatively legible across each row in the lower half. Text with and without the use of font-size-adjust The value of font-size-adjust affects the used value of font-size but does not affect the computed value. Therefore it can affect the size of relative units that are based on font metrics such as ex and ch but does not affect the size of em units. Since numeric values of line-height refer to the computed size of font-size , font-size-adjust also does not affect the used value of line-height . Note: Since font-size-adjust does not factor into the line-height , specifying a line height too tightly can result in overlapping lines of text. For example, when a fallback font with a low aspect value is normalized to match one with a high aspect value , its ascenders and descenders are likely to extend outside the line box with line-height: 1 . The font-size-adjust adjustment applies to any font that is selected but in typical usage it would be based on the corresponding metric value of the first (most desired) font in the font-family list. If this is specified accurately, the ( m / m′ ) term in the adjustment formula will resolve to 1 for the first font and no adjustment occurs for that font; and the rest of the fonts will resolve to match. If the value is specified inaccurately, text rendered using the first font in the family list will display differently in older user agents that don’t support font-size-adjust . Authors can calculate the aspect value for a given font by comparing spans with the same content but different font-size-adjust properties. If the same font-size is used, the spans will match when the font-size-adjust value is accurate for the given font. Two spans with borders are used to determine the aspect value of a font. The font-size is the same for both spans but the font-size-adjust property is specified only for the right span. Starting with a value of 0.5, the aspect value can be adjusted until the borders around the two letters line up. p { font-family : Futura ; font-size : 500 px ; } span { border : solid 1 px red ; } .adjust { font-size-adjust : 0.5 ; } <p><span>b</span><span class= "adjust" >b</span></p> Futura with an aspect value of 0.5 The box on the right is a bit bigger than the one on the left, so the aspect value of this font is something less than 0.5. Adjust the value until the boxes align. Note: If the specified metric has been overridden in @font-face , e.g. by size-adjust , then the overridden metric will be used in the font-size-adjust calculation. Consequently, applying font-size-adjust and size-adjust together means that size-adjust appears to have no effect. 4. Font Resources 4.1. The @font-face rule Note: Descriptors are applied per-font rather than per-element. Multiple fonts can be used within an individual element e.g. for characters not supported by the first available font . 4.2. Font reference: the src descriptor 4.2.1. Parsing the src descriptor The src descriptor value must be parsed according to section CSS Syntax 3 § 5.3.11 Parse a comma-separated list of component values . Then each component value is parsed according to this grammar: <url> [ format ( <font-format> )] ? [ tech ( <font-tech> # )] ? | local ( <font-family-name> ) <font-format> = [ <string> | collection | embedded-opentype | opentype | svg | truetype | woff | woff2 ] <font-tech> = [ <font-features-tech> | <color-font-tech> | variations | palettes | incremental ] <font-features-tech> = [ features-opentype | features-aat | features-graphite ] <color-font-tech> = [ color-COLRv0 | color-COLRv1 | color-SVG | color-sbix | color-CBDT ] If a component value is parsed correctly and is a supported CSS Fonts 4 § 11.2 Font formats or CSS Fonts 4 § 11.1 Font tech , add it to the list of supported sources. If parsing a component value results in a parsing error or its format or tech are unsupported, do not add it to the list of supported sources. If there are no supported entries at the end of this process, the value for the src descriptor is a parse error. These parsing rules allow for graceful fallback of fonts for user agents which don’t support a particular font tech or font format. For example, when incremental transfer is not supported, a woff2 compressed version of the font is supplied, for optimal performance. Then, for incremental transfer , the raw uncompressed OpenType font is provided, portions of which will be loaded on demand. @font-face { font-family : "MyIncrementallyLoadedWebFont" ; src : url ( "FallbackURLForBrowsersWhichDontSupportIncrementalLoading.woff2" ) format ( "woff2" ); src : url ( "MyIncrementallyLoadedWebFont.otf" ) format ( opentype ) tech ( incremental ); } 4.3. Font property descriptors: the font-size w3c/csswg-drafts/806 [css-fonts-5] Add font-size descriptor to @font-face which allows ranges (for optical sizing) w3c/csswg-drafts/731 [css-fonts] font-size Descriptor for ex Unit Name: font-size For: @font-face Value: auto | [ <number> ] {1,2} Initial: auto auto The font matches any font size <number> If a single <number> is given the font matches that specific font size, only. If two <number> s are given, they specify a range of font sizes which will match. 4.4. Glyph Size Multiplier: the size-adjust descriptor Name: size-adjust For: @font-face Value: <percentage [0,∞]> Initial: 100% The size-adjust descriptor defines a multiplier for glyph outlines and metrics associated with this font, to allow the author to harmonize the designs of various fonts when rendered at the same font-size . All metrics associated with this font—including glyph advances, baseline tables, and overrides provided by @font-face descriptors—are scaled by the given percentage, as are the rendered glyph images. Consequently, any values derived from font metrics (such as ex and ch units, or the from-font value of text-decoration-thickness ) are also affected when sourced from this font. However, the computed font-size (and thus any values that derive from it, such as em units, percentages in text-underline-offset , etc.) remains unaffected. Note: The size-adjust descriptor functions similarly to the font-size-adjust property, which essentially calculates an adjustment per font by matching ex heights, but likewise does not affect the computed font-size . Tests font-size-adjust-metrics-override.html (live test) (source) size-adjust-01.html (live test) (source) size-adjust-02.html (live test) (source) size-adjust-03.html (live test) (source) 4.5. Line Height Font Metrics Overrides: the ascent-override , descent-override , and line-gap-override descriptors Name: ascent-override For: @font-face Value: [ normal | <percentage [0,∞]> ] {1,2} Initial: normal Name: descent-override For: @font-face Value: [ normal | <percentage [0,∞]> ] {1,2} Initial: normal Name: line-gap-override For: @font-face Value: [ normal | <percentage [0,∞]> ] {1,2} Initial: normal The ascent-override , descent-override , and line-gap-override descriptors specify the ascent metric , descent metric , and line gap metric of the font, respectively. The first value provides the value for the x axis, and the second value provides the value for the y axis (defaulting to normal if omitted). normal The corresponding metric value is obtained from the font as usual, as if this descriptor were absent from the @font-face block. Note: Since there are multiple sources of such metrics in some font formats, this can result in text layout that varies across UAs/platforms. <percentage> The corresponding metric is replaced by the given percentage multiplied by the effective font size after adjustment. Tests ascent-descent-override.html (live test) (source) font-size-adjust-metrics-override.html (live test) (source) line-gap-override.html (live test) (source) metrics-override-normal-keyword.html (live test) (source) font-face-metric-overrides.html (live test) (source) The font-size-adjust property is applied after the size-adjust descriptor. Note: The consequence of applying font-size-adjust after size-adjust is that size-adjust appears to have no effect. Note: None of these descriptors affect the computation of font-size , line-height , or font-relative lengths . They can, however, affect the behavior of line-height: normal and more generally the baseline alignment of inline-level content. Note: Since these metrics are only applicable in the block axis , the y-axis value will only be used when typesetting upright in vertical typographic modes . The percentage is resolved against different font sizes for different elements. @font-face { font-family : overridden-font ; ascent-override : 50 % ; ... } <span style= "font-family: overridden-font; font-size: 20px;" > Outer span content <span style= "font-size: 150%;" >Inner span content</span> </span> The outer span uses an ascent value of 10px, whereas the inner span uses 15px. We may override the metrics of a local fallback font to match the primary font, which is a web font. This reduces layout shifting when switching from fallback to the primary font. @font-face { font-family : cool-web-font ; src : url ( "https://example.com/font.woff" ); } @font-face { font-family : fallback-to-local ; src : local ( Some Local Font ); /* Override metric values to match cool-web-font */ ascent-override: 125 % ; descent-override : 25 % ; line-gap-override : 0 % ; size-adjust : 96 % ; } <div style= "font-family: cool-web-font, fallback-to-local" >Title goes here</div> <img src= "https://example.com/largeimage" alt= "A large image that you don't want to shift" > The image will not be shifted as much when the user agent finishes loading and switches to use the web font (assuming the override values are similar to the web font’s natural metrics). 4.6. Superscript and subscript metrics overrides: the superscript-position-override , subscript-position-override , superscript-size-override and subscript-size-override descriptors Name: superscript-position-override For: @font-face Value: [ normal | from-font | <percentage> ] {1,2} Initial: normal Name: subscript-position-override For: @font-face Value: [ normal | from-font | <percentage> ] {1,2} Initial: normal Name: superscript-size-override For: @font-face Value: [ normal | from-font | <percentage [0,∞]> ] {1,2} Initial: normal Name: subscript-size-override For: @font-face Value: [ normal | from-font | <percentage [0,∞]> ] {1,2} Initial: normal The superscript-position-override , subscript-position-override , superscript-size-override , and subscript-size-override descriptors specify the superscript offset, subscript offset, superscript size, and subscript size metrics of the font, respectively, which are used to synthesize glyphs when required by font-variant-position . The first value provides the value for the x axis, and the second value provides the value for the y axis (defaulting to the first value if omitted). normal The UA determines what metrics value to use, whether derived from the font or from some heuristic. from-font The corresponding metric in the font data is used, if any. (If the metric is missing, same as normal .) <percentage> The corresponding metric is replaced by the given percentage multiplied by the used font size. Note: Since these metrics are only applicable in the block axis , the y-axis value will only be used when typesetting upright in vertical typographic modes . 5. Font Feature Properties 5.1. Font language override: the font-language-override property w3c/csswg-drafts/5484 [css-fonts-5] Removing font-language-override 6. Font Feature and Variation Resolution w3c/csswg-drafts/5635 [CSS-Fonts] Need method to interpolate variable font settings 7. Font Variation Properties 7.1. Optical sizing control: the font-optical-sizing property w3c/csswg-drafts/5466 [css-text][css-fonts] Optical bounds of a line 8. Font Technologies and Formats 8.1. Font tech This section expands upon CSS Fonts 4 § 11.1 Font tech . The avar2 tech refers to support for version 2 of OpenType axis variations [avar2] , for flexible variation axis remapping. For example, a font using variation axis remapping is loaded only if supported: @font-face { font-family : 'Roboto Flex' ; src : url ( 'RobotoFlex-VF-avar2.woff2' ) format ( woff2 ) tech ( variations , avar2 ); src : url ( 'RobotoFlex-VF.woff2' ) format ( woff2 ) tech ( variations ); font-weight : 100 1000 ; font-stretch : 25 % 151 % ; } 9. Object Model This section expands upon CSS Fonts 4 § 12. Object Model . The contents of @font-face and @font-feature-values rules can be accessed via the following extensions to the CSS Object Model. Tests idlharness.html (live test) (source) 9.1. The CSSFontFaceRule interface The CSSFontFaceRule interface represents a <@font-face> rule. [ Exposed = Window ] interface CSSFontFaceDescriptors : CSSStyleDeclaration { attribute [ LegacyNullToEmptyString ] CSSOMString src ; attribute [ LegacyNullToEmptyString ] CSSOMString fontFamily ; attribute [ LegacyNullToEmptyString ] CSSOMString font-family ; attribute [ LegacyNullToEmptyString ] CSSOMString fontStyle ; attribute [ LegacyNullToEmptyString ] CSSOMString font-style ; attribute [ LegacyNullToEmptyString ] CSSOMString fontWeight ; attribute [ LegacyNullToEmptyString ] CSSOMString font-weight ; attribute [ LegacyNullToEmptyString ] CSSOMString fontStretch ; attribute [ LegacyNullToEmptyString ] CSSOMString font-stretch ; attribute [ LegacyNullToEmptyString ] CSSOMString fontWidth ; attribute [ LegacyNullToEmptyString ] CSSOMString font-width ; attribute [ LegacyNullToEmptyString ] CSSOMString fontSize ; attribute [ LegacyNullToEmptyString ] CSSOMString font-size ; attribute [ LegacyNullToEmptyString ] CSSOMString sizeAdjust ; attribute [ LegacyNullToEmptyString ] CSSOMString size-adjust ; attribute [ LegacyNullToEmptyString ] CSSOMString unicodeRange ; attribute [ LegacyNullToEmptyString ] CSSOMString unicode-range ; attribute [ LegacyNullToEmptyString ] CSSOMString fontFeatureSettings ; attribute [ LegacyNullToEmptyString ] CSSOMString font-feature-settings ; attribute [ LegacyNullToEmptyString ] CSSOMString fontVariationSettings ; attribute [ LegacyNullToEmptyString ] CSSOMString font-variation-settings ; attribute [ LegacyNullToEmptyString ] CSSOMString fontNamedInstance ; attribute [ LegacyNullToEmptyString ] CSSOMString font-named-instance ; attribute [ LegacyNullToEmptyString ] CSSOMString fontDisplay ; attribute [ LegacyNullToEmptyString ] CSSOMString font-display ; attribute [ LegacyNullToEmptyString ] CSSOMString fontLanguageOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString font-language-override ; attribute [ LegacyNullToEmptyString ] CSSOMString ascentOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString ascent-override ; attribute [ LegacyNullToEmptyString ] CSSOMString descentOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString descent-override ; attribute [ LegacyNullToEmptyString ] CSSOMString lineGapOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString line-gap-override ; attribute [ LegacyNullToEmptyString ] CSSOMString superscriptPositionOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString superscript-position-override ; attribute [ LegacyNullToEmptyString ] CSSOMString subscriptPositionOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString subscript-position-override ; attribute [ LegacyNullToEmptyString ] CSSOMString superscriptSizeOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString superscript-size-override ; attribute [ LegacyNullToEmptyString ] CSSOMString subscriptSizeOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString subscript-size-override ; };
[ Exposed = Window ] interface CSSFontFaceRule : CSSRule { [ SameObject , PutForwards = cssText ] readonly attribute CSSFontFaceDescriptors style ; }; 10. Security Considerations No new security considerations have been reported on this specification. 11. Privacy Considerations No new privacy considerations have been reported on this specification. 12. Acknowledgments Firstly, the editors would like to thank all of the contributors to the previous level of this module . Secondly, we would like to acknowledge Dave Crossland from Google, Bernhard Fey from RealObjects, Xiaocheng Hu from Google, Jonathan Kew from Mozilla, and Laurence Penney for their contributions to the improvements in this Level 5. 13. Changes 13.1. Changes since the WD of 6 February 2024 Added text-scale meta tag and preferred-text-scale environment variable support, with example ( Issue 12380 ), ( Issue 12475 ) Added missing CSSOM superscript-position-override, subscript-position-override, superscript-size-override and subscript-size-override descriptors Added missing CSSOM size-adjust and font-size descriptors Added the avar2 font tech ( Issue 10599 ) Updated incremental example to latest IFT spec ( Issue 6063 ) Explicitly stated that font-size-adjust precedes font metrics overrides ( Issue 8967 ) 13.2. Changes since the WD of 21 December 2021 Corrected the initial value for the font-size descriptor Set a range for the grammar of font-size-adjust number Changed grammar of local() to use family-name instead for font-face-name Updated to current incremental font download keywords Made feature-* plural for consistency with CSS Conditional 5, and 11.1 Font tech Normalized infinity to ∞ in range notation Fixed a typo in the tech() function 13.3. Changes since the WD of 2021-07-29 Renamed technology to tech Security and Privacy are now separate sections Fixed font-technology grammar Copied section on parsing src descriptor from CSS Fonts 4 13.4. Changes since the FPWD of 2021-06-29 Removed scary warning notice Added incremental font technology to supports Conformance Document conventions Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification. All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119] Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class= "example" , like this: This is an example of an informative example. Informative notes begin with the word “Note” and are set apart from the normative text with class= "note" , like this: Note, this is an informative note. Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class= "advisement" > , like this: UAs MUST provide an accessible alternative. Tests Tests relating to the content of this specification may be documented in “Tests” blocks like this one. Any such block is non-normative. Conformance classes Conformance to this specification is defined for three conformance classes: style sheet A CSS style sheet . renderer A UA that interprets the semantics of a style sheet and renders documents that use them. authoring tool A UA that writes a style sheet. A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module. A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.) An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module. Partial implementations So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate ) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored. Implementations of Unstable and Proprietary Features To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS. Non-experimental implementations Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec. To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group. Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at https://www.w3.org/Style/CSS/Test/ . Questions should be directed to the [email protected] mailing list. Index Terms defined by this specification ascent-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.5 ascentOverride , in § 9.1 aspect value , in § 3.4 auto , in § 4.3 avar2 , in § 8.1 cap-height , in § 3.4 ch-width , in § 3.4 <color-font-tech> , in § 4.2.1 CSSFontFaceDescriptors , in § 9.1 CSSFontFaceRule (interface) , in § 9.1 definition of , in § 9.1 descent-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.5 descentOverride , in § 9.1 ex-height , in § 3.4 ex-height | cap-height | ch-width | ic-width | ic-height , in § 3.4 font-display , in § 9.1 fontDisplay , in § 9.1 @font-face , in § 4.1 font-family , in § 9.1 fontFamily , in § 9.1 font-feature-settings , in § 9.1 fontFeatureSettings , in § 9.1 <font-features-tech> , in § 4.2.1 <font-format> , in § 4.2.1 font-language-override , in § 9.1 fontLanguageOverride , in § 9.1 font-named-instance , in § 9.1 fontNamedInstance , in § 9.1 font-size attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.3 fontSize , in § 9.1 font-size-adjust , in § 3.4 font-stretch , in § 9.1 fontStretch , in § 9.1 font-style , in § 9.1 fontStyle , in § 9.1 <font-tech> , in § 4.2.1 font-variation-settings , in § 9.1 fontVariationSettings , in § 9.1 font-weight , in § 9.1 fontWeight , in § 9.1 font-width , in § 9.1 fontWidth , in § 9.1 from-font value for font-size-adjust , in § 3.4 value for superscript-position-override!!descriptor, subscript-position-override!!descriptor, superscript-size-override!!descriptor, subscript-size-override!!descriptor , in § 4.6 ic-height , in § 3.4 ic-width , in § 3.4 legacy , in § 2.1 line-gap-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.5 lineGapOverride , in § 9.1 none , in § 3.4 normal value for ascent-override!!descriptor, descent-override!!descriptor, line-gap-override!!descriptor , in § 4.5 value for superscript-position-override!!descriptor, subscript-position-override!!descriptor, superscript-size-override!!descriptor, subscript-size-override!!descriptor , in § 4.6 <number> , in § 4.3 <number [0,∞]> , in § 3.4 <percentage> value for ascent-override!!descriptor, descent-override!!descriptor, line-gap-override!!descriptor , in § 4.5 value for superscript-position-override!!descriptor, subscript-position-override!!descriptor, superscript-size-override!!descriptor, subscript-size-override!!descriptor , in § 4.6 scale , in § 2.1 size-adjust attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.4 sizeAdjust , in § 9.1 src , in § 9.1 style , in § 9.1 subscript-position-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.6 subscriptPositionOverride , in § 9.1 subscript-size-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.6 subscriptSizeOverride , in § 9.1 superscript-position-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.6 superscriptPositionOverride , in § 9.1 superscript-size-override attribute for CSSFontFaceDescriptors , in § 9.1 descriptor for @font-face , in § 4.6 superscriptSizeOverride , in § 9.1 text-scale , in § 2 text scale factor , in § 2 unicode-range , in § 9.1 unicodeRange , in § 9.1 xxx , in § 3.1.1 Terms defined by reference [CSS-CASCADE-5] defines the following terms: computed value used value [CSS-DISPLAY-4] defines the following terms: inline-level [CSS-ENV-1] defines the following terms: preferred-text-scale [CSS-FONTS-4] defines the following terms: <absolute-size> <font-family-name> @font-feature-values first available font font-family font-language-override font-optical-sizing font-size font-style font-variant-position font-weight src [CSS-INLINE-3] defines the following terms: ascent metric descent metric line gap metric [CSS-TEXT-DECOR-4] defines the following terms: from-font text-decoration-thickness text-underline-offset [CSS-TRANSFORMS-2] defines the following terms: scale [CSS-VALUES-4] defines the following terms: <number> <percentage> <string> <url> ? ch CSS-wide keywords em ex font-relative lengths rem {A,B} | [CSS-WRITING-MODES-4] defines the following terms: block axis typesetting upright typographic mode vertical typographic mode [CSS2] defines the following terms: line-height medium [CSSOM-1] defines the following terms: CSSOMString CSSRule CSSStyleDeclaration [HTML] defines the following terms: content meta name [INFRA] defines the following terms: ASCII case-insensitive [SELECTORS-4] defines the following terms: :root [WEBIDL] defines the following terms: Exposed LegacyNullToEmptyString PutForwards SameObject References Normative References [AVAR2] avar — Axis Variations Table Version 2 . 2022. URL: https://github.com/harfbuzz/boring-expansion-spec/blob/main/avar2.md [CSS-CASCADE-5] Elika Etemad; Miriam Suzanne; Tab Atkins Jr.. CSS Cascading and Inheritance Level 5 . 13 January 2022. CR. URL: https://www.w3.org/TR/css-cascade-5/ [CSS-ENV-1] CSS Environment Variables Module Level 1 . 23 September 2025. FPWD. URL: https://www.w3.org/TR/css-env-1/ [CSS-FONTS-4] Chris Lilley. CSS Fonts Module Level 4 . 22 April 2026. WD. URL: https://www.w3.org/TR/css-fonts-4/ [CSS-INLINE-3] Elika Etemad. CSS Inline Layout Module Level 3 . 18 December 2024. WD. URL: https://www.w3.org/TR/css-inline-3/ [CSS-SIZE-ADJUST-1] CSS Mobile Text Size Adjustment Module Level 1 . Editor's Draft. URL: https://drafts.csswg.org/css-size-adjust-1/ [CSS-SYNTAX-3] Tab Atkins Jr.; Simon Sapin. CSS Syntax Module Level 3 . 24 December 2021. CRD. URL: https://www.w3.org/TR/css-syntax-3/ [CSS-TEXT-DECOR-4] Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 4 . 4 May 2022. WD. URL: https://www.w3.org/TR/css-text-decor-4/ [CSS-TRANSFORMS-2] Tab Atkins Jr.; et al. CSS Transforms Module Level 2 . 9 November 2021. WD. URL: https://www.w3.org/TR/css-transforms-2/ [CSS-VALUES-3] Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3 . 22 March 2024. CRD. URL: https://www.w3.org/TR/css-values-3/ [CSS-VALUES-4] Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 4 . 12 March 2024. WD. URL: https://www.w3.org/TR/css-values-4/ [CSS2] Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification . 7 June 2011. REC. URL: https://www.w3.org/TR/CSS2/ [CSSOM-1] Daniel Glazman; Emilio Cobos Álvarez. CSS Object Model (CSSOM) . 26 August 2021. WD. URL: https://www.w3.org/TR/cssom-1/ [HTML] Anne van Kesteren; et al. HTML Standard . Living Standard. URL: https://html.spec.whatwg.org/multipage/ [INFRA] Anne van Kesteren; Domenic Denicola. Infra Standard . Living Standard. URL: https://infra.spec.whatwg.org/ [RFC2119] S. Bradner. Key words for use in RFCs to Indicate Requirement Levels . March 1997. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc2119 [WEBIDL] Edgar Chen; Timothy Gu. Web IDL Standard . Living Standard. URL: https://webidl.spec.whatwg.org/ Non-Normative References [CSS-DISPLAY-4] Elika Etemad; Tab Atkins Jr.. CSS Display Module Level 4 . 6 November 2025. WD. URL: https://www.w3.org/TR/css-display-4/ [CSS-WRITING-MODES-4] Elika Etemad; Koji Ishii. CSS Writing Modes Level 4 . 30 July 2019. CR. URL: https://www.w3.org/TR/css-writing-modes-4/ [SELECTORS-4] Elika Etemad; Tab Atkins Jr.. Selectors Level 4 . 22 January 2026. WD. URL: https://www.w3.org/TR/selectors-4/ Property Index Name Value Initial Applies to Inh. %ages Animation type Canonical order Computed value font-size-adjust none | [ ex-height | cap-height | ch-width | ic-width | ic-height ]? [ from-font | <number [0,∞]> ] none all elements and text yes N/A discrete if the keywords differ, otherwise by computed value type per grammar the keyword none, or a pair of a metric keyword and a <number> @font-face Descriptors Name Value Initial ascent-override [ normal | <percentage [0,∞]> ]{1,2} normal descent-override [ normal | <percentage [0,∞]> ]{1,2} normal font-size auto | [<number>]{1,2} auto line-gap-override [ normal | <percentage [0,∞]> ]{1,2} normal size-adjust <percentage [0,∞]> 100% subscript-position-override [ normal | from-font | <percentage> ]{1,2} normal subscript-size-override [ normal | from-font | <percentage [0,∞]> ]{1,2} normal superscript-position-override [ normal | from-font | <percentage> ]{1,2} normal superscript-size-override [ normal | from-font | <percentage [0,∞]> ]{1,2} normal IDL Index [ Exposed = Window ] interface CSSFontFaceDescriptors : CSSStyleDeclaration { attribute [ LegacyNullToEmptyString ] CSSOMString src ; attribute [ LegacyNullToEmptyString ] CSSOMString fontFamily ; attribute [ LegacyNullToEmptyString ] CSSOMString font-family ; attribute [ LegacyNullToEmptyString ] CSSOMString fontStyle ; attribute [ LegacyNullToEmptyString ] CSSOMString font-style ; attribute [ LegacyNullToEmptyString ] CSSOMString fontWeight ; attribute [ LegacyNullToEmptyString ] CSSOMString font-weight ; attribute [ LegacyNullToEmptyString ] CSSOMString fontStretch ; attribute [ LegacyNullToEmptyString ] CSSOMString font-stretch ; attribute [ LegacyNullToEmptyString ] CSSOMString fontWidth ; attribute [ LegacyNullToEmptyString ] CSSOMString font-width ; attribute [ LegacyNullToEmptyString ] CSSOMString fontSize ; attribute [ LegacyNullToEmptyString ] CSSOMString font-size ; attribute [ LegacyNullToEmptyString ] CSSOMString sizeAdjust ; attribute [ LegacyNullToEmptyString ] CSSOMString size-adjust ; attribute [ LegacyNullToEmptyString ] CSSOMString unicodeRange ; attribute [ LegacyNullToEmptyString ] CSSOMString unicode-range ; attribute [ LegacyNullToEmptyString ] CSSOMString fontFeatureSettings ; attribute [ LegacyNullToEmptyString ] CSSOMString font-feature-settings ; attribute [ LegacyNullToEmptyString ] CSSOMString fontVariationSettings ; attribute [ LegacyNullToEmptyString ] CSSOMString font-variation-settings ; attribute [ LegacyNullToEmptyString ] CSSOMString fontNamedInstance ; attribute [ LegacyNullToEmptyString ] CSSOMString font-named-instance ; attribute [ LegacyNullToEmptyString ] CSSOMString fontDisplay ; attribute [ LegacyNullToEmptyString ] CSSOMString font-display ; attribute [ LegacyNullToEmptyString ] CSSOMString fontLanguageOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString font-language-override ; attribute [ LegacyNullToEmptyString ] CSSOMString ascentOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString ascent-override ; attribute [ LegacyNullToEmptyString ] CSSOMString descentOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString descent-override ; attribute [ LegacyNullToEmptyString ] CSSOMString lineGapOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString line-gap-override ; attribute [ LegacyNullToEmptyString ] CSSOMString superscriptPositionOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString superscript-position-override ; attribute [ LegacyNullToEmptyString ] CSSOMString subscriptPositionOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString subscript-position-override ; attribute [ LegacyNullToEmptyString ] CSSOMString superscriptSizeOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString superscript-size-override ; attribute [ LegacyNullToEmptyString ] CSSOMString subscriptSizeOverride ; attribute [ LegacyNullToEmptyString ] CSSOMString subscript-size-override ; };
[ Exposed = Window ] interface CSSFontFaceRule : CSSRule { [ SameObject , PutForwards = cssText ] readonly attribute CSSFontFaceDescriptors style ; }; Issues Index w3c/csswg-drafts/126 [css-fonts] Specifying changes to parameters for fallback fonts ↵ w3c/csswg-drafts/4910 [meta] [css-fonts] Criteria for generic font families ↵ w3c/csswg-drafts/4566 [css-fonts] Should we start a registry for additional generic fonts? ↵ w3c/csswg-drafts/2690 [css-fonts-4] Percentages in font-weight for relative weights ↵ w3c/csswg-drafts/4044 [css-fonts] Vertical text doesn't play nicely with font-style and font-stretch ↵ w3c/csswg-drafts/8792 [css-fonts-5] font-size-adjust: ic-height ↵ w3c/csswg-drafts/6384 [css-fonts-5] font-size-adjust with missing metrics ↵ w3c/csswg-drafts/806 [css-fonts-5] Add font-size descriptor to @font-face which allows ranges (for optical sizing) ↵ w3c/csswg-drafts/731 [css-fonts] font-size Descriptor for ex Unit ↵ w3c/csswg-drafts/5484 [css-fonts-5] Removing font-language-override ↵ w3c/csswg-drafts/5635 [CSS-Fonts] Need method to interpolate variable font settings ↵ w3c/csswg-drafts/5466 [css-text][css-fonts] Optical bounds of a line ↵