The following rules always hold:
In CSS, identifiers + (including element names, classes, and IDs + in selectors) can contain only the + characters [a-zA-Z0-9] and ISO 10646 characters U+00A1 and higher, plus the hyphen (-) and the underscore (_); they cannot start with - a digit, or a hyphen followed by a digit. - Identifiers can also contain escaped characters and any ISO 10646 - character as a numeric code (see next item). + a digit, or a hyphen followed by a digit. Identifiers can also + contain escaped characters and any ISO 10646 character as a + numeric code (see next item). For instance, the identifier "B&W?" may - be written as "B\&W\?" or "B\26 W\3F". + be written as "B\&W\?" or "B\26 W\3F".
Note that Unicode is code-by-code equivalent to ISO 10646 (see [UNICODE] and [ISO10646]). -
-First, inside a string, a backslash - followed by a newline is ignored (i.e., the string is deemed not - to contain either the backslash or the newline). -
-Second, it cancels the meaning of special CSS characters. - Except within CSS comments, any character (except a - hexadecimal digit, linefeed, carriage return, or form feed) - can be escaped - with a backslash to remove its special meaning. - For example, "\"" is a string consisting of one - double quote. Style sheet preprocessors must not remove - these backslashes from a style sheet since that would - change the style sheet's meaning. -
-Third, backslash escapes allow authors to refer to characters - they cannot easily put in a document. In this case, the backslash - is followed by at most six hexadecimal digits (0..9A..F), which - stand for the ISO 10646 ([ISO10646]) - character with that number, which must not be zero. - (It is undefined in CSS 2.1 what happens if a style sheet - does contain a character with Unicode codepoint zero.) - If a character in the range [0-9a-fA-F] follows the hexadecimal number, - the end of the number needs to be made clear. There are two ways - to do that: -
+Backslash (\) characters are not significant inside + comments. Elsewhere, they + introduce character + escapes.
+ +Some character escapes have the effect of inserting a + character into the style sheet, in place of the escape. + Whenever this happens, the inserted character is treated as + either part of an identifier, or part of a string, even if it + normally would have some special meaning. See the examples + below.
+ +If a backslash is immediately followed by the end of the + style sheet, it is a normal character, not an escape.
+Within strings, a backslash + followed by a newline is ignored; i.e., the string continues + on the next line, but with neither the backslash nor the + newline included in the string's value. Outside strings, a + backslash followed by a newline is a normal punctuation + character.
A backslash followed by one to six hexadecimal digits, + [0-9a-fA-F], inserts the ISO 10646 + ([ISO10646]) + character with that number into the style sheet.
+ +One (and only one) white space character is ignored after a + hexadecimal escape of any length. This rule allows authors to + write hexadecimal escapes that are immediately followed by + characters from the set [0-9a-fA-F], without ambiguity. For + instance, "\26 B", + "\000026B", and "\000026 B" are + all equivalent to "&B". + However, "\26B" is equivalent + to "ɫ" (a string containing the single + character U+026B).
+ +If a hexadecimal escape would insert the character with + code point U+0000, the behavior is undefined. Hexadecimal + escapes that are outside the range allowed by Unicode + (e.g. "\110000" stands for a character above the current limit + of U+10FFFF) may be treated as inserting the "replacement + character" (U+FFFD). If such characters are to be displayed, + the UA should show a visible symbol, such as a "missing + character" glyph (cf. 15.2, + point 5).
A backslash followed by any other character (neither a + hexadecimal digit nor a newline) simply removes that + character's special meaning. For instance, "\"" + is a string consisting of one double quote, a\:b + is an identifier consisting of the three characters + a:b, and "te\nt" is exactly the + same string as "tent". \7B is not + punctuation, even though { is, + and \32 is allowed at the start of an + identifier, even though 2 is not).
In fact, these two methods may be combined. Only one white space - character is ignored after a hexadecimal escape. Note that this means - that a "real" space after the escape sequence must itself either be - escaped or doubled. -
-If the number is outside the range allowed by Unicode (e.g., - "\110000" is above the maximum 10FFFF allowed in current Unicode), - the UA may replace the escape with the "replacement character" - (U+FFFD). If the character is to be displayed, the UA should show - a visible symbol, such as a "missing character" glyph (cf. 15.2, point 5). -
The identifier "te\st" is exactly the same identifier as "test". -
Style sheet preprocessors are free to convert + escape sequences to the equivalent characters, or vice versa, as + long as they do not change the style sheet's meaning. For + instance, "\61 b" may be rewritten as "ab"; "a\3a b" may be + rewritten as "a\:b" or vice versa, but not "a:b".
+ +