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[css-fonts-4] Move font-tech & font-format to new section
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‎css-fonts-4/Overview.bs‎

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@@ -2176,105 +2176,12 @@ for user agents which don't support a particular font technology.
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</pre>
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</div>
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<h5 id="font-face-src-format-types">''@font-face'' format types</h5>
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Format strings defined by this specification are as follows.
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The <<font-format>> values are synonyms for the formats below.
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<table class="data" id="fontformats">
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<thead>
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<tr>
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<th>String
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<th>Font Format
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<th>Common extensions
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<tbody>
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<tr>
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<th>"woff"
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<td><a href="https://www.w3.org/TR/WOFF/">WOFF (Web Open Font Format)</a>
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<td>.woff
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<tr>
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<th>"truetype"
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<td><a href="https://www.microsoft.com/typography/otspec/default.htm">TrueType</a>
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<td>.ttf
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<tr>
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<th>"opentype"
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<td><a href="https://www.microsoft.com/typography/otspec/default.htm">OpenType</a>
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<td>.ttf, .otf
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<tr>
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<th>"woff2"
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<td><a href="https://www.w3.org/TR/WOFF2/">WOFF File Format 2.0 (Web Open Font Format)</a>
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<td>.woff2
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<tr>
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<th>"embedded-opentype"
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<td><a href="https://www.w3.org/Submission/2008/SUBM-EOT-20080305/">Embedded OpenType</a>
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<td>.eot
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<tr>
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<th>"collection"</th>
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<td><a href="https://docs.microsoft.com/en-us/typography/opentype/spec/otff#collections">OpenType Collection</a></td>
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<td>.otc,.ttc</td>
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</tr>
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<tr>
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<th>"svg"
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<td><a href="https://www.w3.org/TR/SVG11/fonts.html">SVG Font</a> (deprecated)
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<td>.svg, .svgz
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</table>
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Given the overlap in common usage between TrueType and OpenType,
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the format hints "truetype" and "opentype"
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must be considered as synonymous;
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a format hint of "opentype" does not imply
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that the font contains Postscript CFF style glyph data
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or that it contains OpenType layout information
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(see <a href="#platform-props-to-css">Appendix A</a> for more background on this).
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<h5 id="font-face-src-requirement-types">''@font-face'' requirements</h5>
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The 'features' requirement refers to support for font features,
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commonly implemented in [[!OPENTYPE]] with the <code>GSUB</code> and the <code>GPOS</code> tables,
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as well as in [[!AAT-FEATURES]] using the <code>morx</code> and <code>kerx</code> tables
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and [[!GRAPHITE]] with the <code>Silf</code>, <code>Glat </code>, <code>Gloc </code>,
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<code>Feat </code> and <code>Sill </code> tables.
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The section on [[#font-rend-props]] describes properties that interact with these facilities.
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The 'variations' requirement refers to the support of font variations,
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commonly implemented in [[!OPENTYPE]] with the
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<code>avar</code>, <code>cvar</code>, <code>fvar</code>, <code>gvar</code>, <code>HVAR</code>, <code>MVAR</code>, <code>STAT</code>, and <code>VVAR</code> tables,
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as well as in [[!AAT-FEATURES]] using the <code>avar</code>, <code>cvar</code>, <code>fvar</code>, and <code>gvar</code> tables.
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The section on [[#basic-font-props]] as well as the section on [[#font-variation-props]]
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describe properties that interact with these facilities.
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The 'color' requirement lists various types of color font file technologies.
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Each of the arguments to the 'color' function represents a table
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inside [[!OPENTYPE]] or [[!AAT-FEATURES]] fonts which must be supported
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to satisfy this requirement.
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The 'palettes' requirement refers to support for font palettes,
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commonly implemented in the [[!OPENTYPE]] and [[!AAT-FEATURES]]
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with the <code>CPAL</code> table.
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The section on [[#color-font-support]] describes properties that interact with these facilities.
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The 'incremental' requirement refers to client support for
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incremental font loading,
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using either the range-request or the patch-subset method [[PFE-report]].
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Web authors can specify the 'format' function
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to indicate that support is
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required for correct rendering of a font.
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This mechanism can be used for gracefully falling back
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to an ancillary font
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when variation support is not present.
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<div class="example">
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This ''@font-face'' block shows how to use a color font if support is present on the user agent,
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and falls back to a non-color-font if support is not present.
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<pre>
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@font-face {
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font-family: "Trickster";
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src: url("trickster-COLRv1.otf") format(opentype supports color(COLRv1)),
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url("trickster-outline.otf") format(opentype);
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}
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</pre>
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</div>
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<!-- font formats and font requirements
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moved from a minor section inside src
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to a new section
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so they can be more easily shared
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with css-conditional-4
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-->
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<h5 id="local-font-fallback">Local font fallback</h5>
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@@ -6753,6 +6660,115 @@ System Font</h3>
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The System Font is the font which is used by the ''system-ui'' <a href="#system-ui-def">generic font family name</a>. It is an example of a Preinstalled Font.
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<h2 id="font-technologies-formats">
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Font Technologies and Formats
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</h2>
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<h3 id="font-technology-definitions">Font technologies</h3>
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The 'features-opentype', 'features-aat' and 'features-graphite' technologies
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refer to support for font features,
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commonly implemented in [[!OPENTYPE]] with the <code>GSUB</code> and the <code>GPOS</code> tables,
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as well as in [[!AAT-FEATURES]] using the <code>morx</code> and <code>kerx</code> tables
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and [[!GRAPHITE]] with the <code>Silf</code>, <code>Glat </code>, <code>Gloc </code>,
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<code>Feat </code> and <code>Sill </code> tables.
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The section on [[#font-rend-props]] describes properties that interact with these facilities.
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The 'variations' technology refers to the support of font variations,
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commonly implemented in [[!OPENTYPE]] with the
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<code>avar</code>, <code>cvar</code>, <code>fvar</code>, <code>gvar</code>, <code>HVAR</code>, <code>MVAR</code>, <code>STAT</code>, and <code>VVAR</code> tables,
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as well as in [[!AAT-FEATURES]] using the <code>avar</code>, <code>cvar</code>, <code>fvar</code>, and <code>gvar</code> tables.
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The section on [[#basic-font-props]] as well as the section on [[#font-variation-props]]
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describe properties that interact with these facilities.
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The 'color-colrv0', 'color-colrv1', 'color-svg', 'color-sbix' and 'color-cbdt'
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technologies refers to various types of color font file technologies.
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Each one represents a table
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(<code>COLR</code>, <code>SVG</code> <code>sbix</code> or <code>cbdt</code>)
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inside [[!OPENTYPE]] or [[!AAT-FEATURES]] fonts which must be supported
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to satisfy this requirement.
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The 'palettes' technology refers to support for font palettes,
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commonly implemented in the [[!OPENTYPE]] and [[!AAT-FEATURES]]
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with the <code>CPAL</code> table.
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The section on [[#color-font-support]] describes properties that interact with these facilities.
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The 'incremental' requirement refers to client support for
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incremental font loading,
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using either the range-request or the patch-subset method [[PFE-report]].
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Web authors can specify the 'technology' function
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inside an ''@font-face'' 'src' descriptor
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to indicate that support is
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required for correct rendering of a font.
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This mechanism can be used for gracefully falling back
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to an ancillary font
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when requested support is not present.
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<div class="example">
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This ''@font-face'' block shows how to use a color font if support is present on the user agent,
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and falls back to a non-color-font if support is not present.
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<pre>
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@font-face {
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font-family: "Trickster";
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src: url("trickster-COLRv1.otf") format(opentype supports color(COLRv1)),
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url("trickster-outline.otf") format(opentype);
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}
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</pre>
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</div>
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<h3 id="font-formatdefinitions">Font formats</h3>
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Format strings defined by this specification are as follows.
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The <<font-format>> values are synonyms for the formats below.
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<table class="data" id="fontformats">
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<thead>
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<tr>
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<th>String
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<th>Font Format
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<th>Common extensions
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<tbody>
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<tr>
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<th>"collection"</th>
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<td><a href="https://docs.microsoft.com/en-us/typography/opentype/spec/otff#collections">OpenType Collection</a></td>
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<td>.otc,.ttc</td>
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<tr>
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<th>"embedded-opentype"
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<td><a href="https://www.w3.org/Submission/2008/SUBM-EOT-20080305/">Embedded OpenType</a>
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<td>.eot
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<tr>
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<th>"opentype"
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<td><a href="https://www.microsoft.com/typography/otspec/default.htm">OpenType</a>
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<td>.ttf, .otf
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<tr>
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<th>"svg"
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<td><a href="https://www.w3.org/TR/SVG11/fonts.html">SVG Font</a> (deprecated)
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<td>.svg, .svgz
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<tr>
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<th>"truetype"
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<td><a href="https://www.microsoft.com/typography/otspec/default.htm">TrueType</a>
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<td>.ttf
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<tr>
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<th>"woff"
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<td><a href="https://www.w3.org/TR/WOFF/">WOFF 1.0 (Web Open Font Format)</a>
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<td>.woff
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<tr>
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<th>"woff2"
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<td><a href="https://www.w3.org/TR/WOFF2/">WOFF 2.0 (Web Open Font Format)</a>
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<td>.woff2
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</table>
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Given the overlap in common usage between TrueType and OpenType,
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the format hints "truetype" and "opentype"
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must be considered as synonymous;
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a format hint of "opentype" does not imply
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that the font contains Postscript CFF style glyph data
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or that it contains OpenType layout information
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(see <a href="#platform-props-to-css">Appendix A</a> for more background on this).
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