Strings are sequences of characters (specifically Unicode code points). Sass supports two kinds of strings whose internal structure is the same but which are rendered differently: quoted strings, like "Helvetica Neue", and unquoted strings (also known as identifiers), like bold. Together, these cover the different kinds of text that appear in CSS.
All Sass strings support the standard CSS escape codes:
Any character other than a letter from A to F or a number from 0 to 9 (even a newline!) can be included as part of a string by writing \ in front of it.
Any character can be included as part of a string by writing \ followed by its Unicode code point number written in hexadecimal. You can optionally include a space after the code point number to indicate where the Unicode number ends.
For characters that are allowed to appear in strings, writing the Unicode escape produces exactly the same string as writing the character itself.
QuotedQuoted permalinkQuoted strings are written between either single or double quotes, as in "Helvetica Neue". They can contain interpolation, as well as any unescaped character except for:
\, which can be escaped as \\;' or ", whichever was used to define that string, which can be escaped as \' or \";\a (including a trailing space).Quoted strings are guaranteed to be compiled to CSS strings that have the same contents as the original Sass strings. The exact format may vary based on the implementation or configuration—a string containing a double quote may be compiled to "\"" or '"', and a non-ASCII character may or may not be escaped. But that should be parsed the same in any standards-compliant CSS implementation, including all browsers.
When a quoted string is injected into another value via interpolation, its quotes are removed! This makes it easy to write strings containing selectors, for example, that can be injected into style rules without adding quotes.
UnquotedUnquoted permalinkUnquoted strings are written as CSS identifiers, following the syntax diagram below. They may include interpolation anywhere.
Railroad diagram copyright © 2018 W3C® (MIT, ERCIM, Keio, Beihang). W3C liability, trademark and permissive document license rules apply. ⚠️ Heads up!Not all identifiers are parsed as unquoted strings:
null is parsed as Sass’s null value.true and false are parsed as Booleans.not, and, and or are parsed as Boolean operators.Because of this, it’s generally a good idea to write quoted strings unless you’re specifically writing the value of a CSS property that uses unquoted strings.
Escapes in Unquoted StringsEscapes in Unquoted Strings permalinkCompatibility (Normalization):
LibSass, Ruby Sass, and older versions of Dart Sass don’t normalize escapes in identifiers. Instead, the text in the unquoted string is the exact text the user wrote. For example, \1F46D and 👠are not considered equivalent.
When an unquoted string is parsed, the literal text of escapes are parsed as part of the string. For example, \a is parsed as the characters \, a, and space. In order to ensure that unquoted strings that have the same meanings in CSS are parsed the same way, though, these escapes are normalized. For each code point, whether it’s escaped or unescaped:
If it’s a valid identifier character, it’s included unescaped in the unquoted string. For example, \1F46D returns the unquoted string đź‘.
If it’s a printable character other than a newline or a tab, it’s included after a \. For example, \21 returns the unquoted string \!.
Otherwise, the lowercase Unicode escape is included with a trailing space. For example, \7Fx returns the unquoted string \7f x.
In addition to identifiers, there are a few unusual corners of CSS syntax that are parsed as unquoted strings. These include:
Special functions like url() and element() whose arguments have syntax that’s different from normal CSS expression syntax.
Unicode range tokens like U+0-7F or U+4??.
Hash tokens whose values are identifiers but which aren’t valid hex colors.
The value %. (This is only available when it’s not directly between two other values, because otherwise it would be ambiguous with the modulo operator.)
The special value !important.
Sass has a number of string functions that take or return numbers, called indexes, that refer to the characters in a string. The index 1 indicates the first character of the string. Note that this is different than many programming languages where indexes start at 0! Sass also makes it easy to refer to the end of a string. The index -1 refers to the last character in a string, -2 refers to the second-to-last, and so on.
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