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145 lines
4.7 KiB
Plaintext
145 lines
4.7 KiB
Plaintext
---
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title: Special Functions
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table_of_contents: true
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introduction: >
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CSS defines many functions, and most of them work just fine with Sass’s normal
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function syntax. They’re parsed as function calls, resolved to [plain CSS
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functions](../at-rules/function#plain-css-functions), and compiled as-is to
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CSS. There are a few exceptions, though, which have special syntax that can’t
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just be parsed as a [SassScript expression](structure#expressions). All
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special function calls return [unquoted strings](../values/strings#unquoted).
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---
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## `url()`
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The [`url()` function][] is commonly used in CSS, but its syntax is different
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than other functions: it can take either a quoted *or* unquoted URL. Because an
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unquoted URL isn't a valid SassScript expression, Sass needs special logic to
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parse it.
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[`url()` function]: https://developer.mozilla.org/en-US/docs/Web/CSS/url
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If the `url()`'s argument is a valid unquoted URL, Sass parses it as-is,
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although [interpolation][] may also be used to inject SassScript values. If it's
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not a valid unquoted URL—for example, if it contains [variables][] or [function
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calls][]—it's parsed as a normal [plain CSS function call][].
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[interpolation]: ../interpolation
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[variables]: ../variables
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[function calls]: ../at-rules/function
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[plain CSS function call]: ../at-rules/function#plain-css-functions
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<% example do %>
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$roboto-font-path: "../fonts/roboto";
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@font-face {
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// This is parsed as a normal function call that takes a quoted string.
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src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2");
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font-family: "Roboto";
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font-weight: 100;
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}
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@font-face {
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// This is parsed as a normal function call that takes an arithmetic
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// expression.
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src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2");
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font-family: "Roboto";
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font-weight: 300;
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}
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@font-face {
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// This is parsed as an interpolated special function.
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src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2");
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font-family: "Roboto";
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font-weight: 400;
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}
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===
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$roboto-font-path: "../fonts/roboto"
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@font-face
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// This is parsed as a normal function call that takes a quoted string.
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src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2")
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font-family: "Roboto"
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font-weight: 100
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@font-face
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// This is parsed as a normal function call that takes an arithmetic
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// expression.
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src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2")
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font-family: "Roboto"
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font-weight: 300
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@font-face
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// This is parsed as an interpolated special function.
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src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2")
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font-family: "Roboto"
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font-weight: 400
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<% end %>
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## `element()`, `progid:...()`, and `expression()`
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<% impl_status dart: "<1.40.0", libsass: false, ruby: false, feature: "calc()" do %>
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LibSass, Ruby Sass, and versions of Dart Sass prior to 1.40.0 parse `calc()`
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as special syntactic function like `element()`.
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Dart Sass versions 1.40.0 and later parse `calc()` as a [calculation].
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[calculation]: ../values/calculations
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<% end %>
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<% impl_status dart: ">=1.31.0 <1.40.0", libsass: false, ruby: false, feature: "clamp()" do %>
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LibSass, Ruby Sass, and versions of Dart Sass prior to 1.31.0 parse `clamp()`
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as a [plain CSS function] rather than supporting special syntax within it.
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[plain CSS function]: ../at-rules/function#plain-css-functions
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Dart Sass versions between 1.31.0 and 1.40.0 parse `clamp()` as special
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syntactic function like `element()`.
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Dart Sass versions 1.40.0 and later parse `clamp()` as a [calculation].
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[calculation]: ../values/calculations
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<% end %>
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The [`element()`] function is defined in the CSS spec, and because its IDs could
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be parsed as colors, they need special parsing.
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[`element()`]: https://developer.mozilla.org/en-US/docs/Web/CSS/element
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[`expression()`][] and functions beginning with [`progid:`][] are legacy
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Internet Explorer features that use non-standard syntax. Although they're no
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longer supported by recent browsers, Sass continues to parse them for backwards
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compatibility.
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[`expression()`]: https://blogs.msdn.microsoft.com/ie/2008/10/16/ending-expressions/
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[`progid:`]: https://blogs.msdn.microsoft.com/ie/2009/02/19/the-css-corner-using-filters-in-ie8/
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Sass allows *any text* in these function calls, including nested parentheses.
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Nothing is interpreted as a SassScript expression, with the exception that
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[interpolation][] can be used to inject dynamic values.
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<% example do %>
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$logo-element: logo-bg;
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.logo {
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background: element(##{$logo-element});
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}
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===
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$logo-element: logo-bg
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.logo
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background: element(##{$logo-element})
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===
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.logo {
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background: element(#logo-bg);
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}
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<% end %>
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