<ident>

A CSS identifier consists of one or more characters, which can be any of the following:

• any ASCII character in the ranges A-Z and a-z
• any decimal digit (0 to 9)
• a hyphen (-)
• an underscore (_)
• any other Unicode character U+00A0 and higher (that is, any other non-ASCII Unicode character)
• an escaped character

Additionally, an identifier must not start with an unescaped digit, and must not start with an unescaped hyphen followed by an unescaped digit.

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

Escaping a character means representing it in a way that changes how it is interpreted by a software system. In CSS, you can escape a character by adding a backslash (\) in front of the character. Any character, except the hexadecimal digits 0-9, a-f, and A-F, can be escaped in this way. For example, & can be escaped as \&.

You can also escape any character with a backslash followed by the character's Unicode code point represented by one to six hexadecimal digits. For example, & can be escaped as \26. In this usage, if the escaped character is followed by a hexadecimal digit, do one of the following:

• Place a space or other whitespace character after the Unicode code point.
• Provide the full six-digit Unicode code point of the character being escaped.

For example, the string &123 can be escaped as \26 123 (with a whitespace) or \000026123 (with the six-digit Unicode code point for &) to ensure that 123 is not considered as part of the escape pattern.

nono79        /* A mix of alphanumeric characters and numbers */
ground-level  /* A mix of alphanumeric characters and a dash */
-test         /* A hyphen followed by alphanumeric characters */
--toto        /* A custom-property like identifier */
_internal     /* An underscore followed by alphanumeric characters */
\22 toto      /* An escaped character followed by alphanumeric characters */
\000022toto   /* Same as the previous example */
bili\.bob     /* A correctly escaped period */
🔥123         /* A non-ASCII character followed by numbers */

34rem     /* Must not start with a decimal digit */
-12rad    /* Must not start with a dash followed by a decimal digit */
bili.bob  /* ASCII characters apart from alphanumerics must be escaped */
'bilibob' /* Treated as a string */
"bilibob" /* Treated as a string */

As this type is not a real type but a convenience type used to simplify the definition of other CSS syntax, there is no browser compatibility information as such.

• <custom-ident>
• <dashed-ident>