user-ident property - CSS Reference

user-ident property CSS Reference

Definition and Usage

The <user-ident> CSS data value denotes an arbitrary user-defined string used as an identifier.

Its syntax is similar to the CSS identifier one, except that it is case-sensitive: a <user-ident> is a sequence of characters where characters can be:

any alphanumeric character (A to Z, or a to z),
any decimal digit (0 to 9),
a dash ('-')
an underscore ('_'),
a escaped character (with a backslash, '\'),
or a Unicode character (in the format of a backslash followed by one to six hexadecimal digits, 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 <user-ident> must not be placed between single or double quotes as it would be identical to a <string>.

Note that id1, Id1, iD1 and ID1 are all different identifiers as they are case-sensitive. In the opposite, as they are several way to escape a character, toto\? and toto\3F are the same identifiers.

These are 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 an alphabetic character
_internal         An underscore followed by alphanumeric characters
\22 toto          A Unicode character followed by a sequence of alphanumeric character
bili\.bob         The period is correctly escaped

These are 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 - need not being escaped.
--toto            It must not start with two dashes.
'bilibob'         It isn't an <user-ident>, it is a <string>.
"bilibob"         It isn't an <user-ident>, it is a <string>.

The <user-ident> data type is mainly used in conjunction with CSS Counters, the counter functional notation and the two related CSS properties, counter-reset and counter-increment.