<custom-ident>

The <custom-ident> CSS data type denotes an arbitrary user-defined string used as an identifier. It is case-sensitive, and certain values are forbidden in various contexts to prevent ambiguity.

Syntax

The syntax of <custom-ident> is similar to CSS identifiers (such as property names), except that it is case-sensitive. A <custom-ident> is a sequence of characters, where characters can be:

• any alphabetical character ('A' to 'Z', or 'a' to 'z'),
• any decimal digit ('0' to '9'),
• a hyphen ('-'),
• an underscore ('_'),
• an escaped character (with a backslash, '\'),
• or a Unicode character (in the format of a backslash followed by one to six hexadecimal digits, representing its Unicode code point).

The first character must not be a decimal digit, nor a dash ('-') followed by a decimal digit or another dash. A <custom-ident> must not be placed between single or double quotes as this would be identical to a <string>.

Note that id1, Id1, iD1 and ID1 are all different identifiers as they are case-sensitive. On the other hand, as there are several ways to escape a character, toto\? and toto\3F are the same identifiers.

Forbidden values

To prevent ambiguity, each property that uses <custom-ident> forbids the use of specific values:

animation-name

Forbids the global CSS values, unset, initial, and inherit, as well as none.

counter-reset

counter-increment

Forbids the global CSS values, unset, initial, and inherit, as well as none.

@counter-style

list-style-type

Forbids the global CSS values, unset, initial, and inherit, as well as the values none, inline, and outside. Also, quite a few predefined values are implemented by the different browsers: disc, circle, square, decimal, cjk-decimal, decimal-leading-zero, lower-roman, upper-roman, lower-greek, lower-alpha, lower-latin, upper-alpha, upper-latin, arabic-indic, armenian, bengali, cambodian, cjk-earthly-branch, cjk-heavenly-stem, cjk-ideographic, devanagari, ethiopic-numeric, georgian, gujarati, gurmukhi, hebrew, hiragana, hiragana-iroha, japanese-formal, japanese-informal, kannada, katakana, katakana-iroha, khmer, korean-hangul-formal, korean-hanja-formal, korean-hanja-informal, lao, lower-armenian, malayalam, mongolian, myanmar, oriya, persian, simp-chinese-formal, simp-chinese-informal, tamil, telugu, thai, tibetan, trad-chinese-formal, trad-chinese-informal, upper-armenian, disclosure-open, and disclosure-close.

grid-row-start
grid-row-end
grid-column-start
grid-column-end

Forbids the span value.

will-change

Forbids the global CSS values, unset, initial, inherit, as well as the values will-change, auto, scroll-position, and contents.

Examples

Valid identifiers

nono79            A mix of alphanumeric characters and numbers
ground-level      A mix of alphanumeric characters and a dash
-test             A dash followed by alphanumeric characters
_internal         An underscore followed by alphanumeric characters
\22 toto          A Unicode character followed by a sequence of alphanumeric characters
bili\.bob         A correctly escaped period

Invalid identifiers

34rem             It must not start with a decimal digit.
-12rad            It must not start with a dash followed by a decimal digit.
bili.bob          Only alphanumeric characters, _, and - needn't be escaped.
--toto            It must not start with two dashes. This would be a custom property.
'bilibob'         This would be a <string>.
"bilibob"         This would be a <string>.

Specifications

Browser compatibility

As this type is not a real type but a convenience type used to simplify the description of allowed values, there is no browser compatibility information as such.

See also

• CSS Data Types: <angle>, <blend-mode>, <color>, <custom-ident>, <frequency>, <gradient>, <image>, <length>, <number>, <percentage>, <position>, <ratio>, <resolution>, <shape>, <string>, <time>, <timing-function>, <uri>