Special Functions
CSS defines many functions, and most of them work just fine with Sass’s normal function syntax. They’re parsed as function calls, resolved to plain CSS functions, and compiled as-is to CSS. There are a few exceptions, though, which have special syntax that can’t just be parsed as a SassScript expression. All special function calls return unquoted strings.
url()
url() permalink
The url()
function is commonly used in CSS, but its syntax is different
than other functions: it can take either a quoted or unquoted URL. Because an
unquoted URL isn’t a valid SassScript expression, Sass needs special logic to
parse it.
If the url()
’s argument is a valid unquoted URL, Sass parses it as-is,
although interpolation may also be used to inject SassScript values. If it’s
not a valid unquoted URL—for example, if it contains variables or function
calls—it’s parsed as a normal plain CSS function call.
element()
, progid:...()
, and expression()
element(), progid:…(), and expression() permalink
- Dart Sass
- since <1.40.0
- LibSass
- ✗
- Ruby Sass
- ✗
- Dart Sass
- since >=1.31.0 <1.40.0
- LibSass
- ✗
- Ruby Sass
- ✗
The element()
function is defined in the CSS spec, and because its IDs could
be parsed as colors, they need special parsing.
expression()
and functions beginning with progid:
are legacy
Internet Explorer features that use non-standard syntax. Although they’re no
longer supported by recent browsers, Sass continues to parse them for backwards compatibility.
Sass allows any text in these function calls, including nested parentheses. Nothing is interpreted as a SassScript expression, with the exception that interpolation can be used to inject dynamic values.