The base character set for CSS is Unicode, a set which allows for
approximately 65,000 characters and extension mechanisms allowing
for millions more.) Keyboards are just not capable of directly
inputing all of these characters. Yet, there will likely be times
when an author wishes to use a character that can not be directly
input from the keyboard. A special new syntax in CSS2 allows for this.
Use of the backslash character ("\") indicates that what
follows is an escape sequence for a Unicode character. The hexadecimal
escape code that follows the backslash represents the desired Unicode
code point. As many as six hexadecimal digits may be specified after the
backslash character, but fewer may be used. Unlike in HTML, character
references in CSS have a beginning delimiter, but no end delimiter other
than the constraint that there will be no MORE than 6 hexadecimal
digits for the reference. For character references LESS than 6
hexadecimal digits in length, appending the value with a white-space
character ensures that the Unicode value reference is properly terminated.
In CSS2, The first trailing white-space character following a Unicode
character reference should be ignored.
The backslash character can also be used to avoid parsing of special
CSS syntax characters (eg: the ";" character can be escaped as "\;".)
Hexadecimal characters can not be escaped this way because they are
interpreted in the manner listed above.
A newline character is ignored in a string value if it is immediately
preceded by the backslash character.
CSS Comments
[CSS1|CSS2|CSS2.1]
[IE3|N4|O3.5|S1]
While Cascading Style Sheet syntax is very self-documenting, there will
be times when an author will want to add explanations or comments in a
style sheet. CSS syntax allows for this. A CSS comment (like in the C
programming language) begins with "/*", and ends with "*/" - everything
that lies between these delimiters is the comment and should be ignored
by the CSS parser. Comments may not be nested and can occur anywhere
between CSS syntax constructs.
Note:
The specification does not seem to be clear on how HTML/XML comment
constructs ("<!-- -->") are treated in CSS syntax.
'!important' Rules
[CSS1|CSS2|CSS2.1]
[IE4|N6|O3.5|S1]
CSS allows both the author and the reader to specify style information
for a document. An author's style sheet will usually contain rules
attempting to preserve the original design intent; a user's style sheet
may contain style rules that are imperative for their viewing needs (eg:
possibly larger font sizes for users with poorer eyesight.)
By default, style rules in an author's style sheet will have higher
precedence than an equivalent style rule in a user's style sheet. This
skews the decision-making of page rendering decidedly towards the author,
which can be very limiting for some users ...to the point of making
content exclusionary in some cases.
CSS allows the scales to be balanced with the "!important" keyword. When
this keyword is added at the end of a style declaration (eg: "h2 { color:
white !important }") it is given higher precedence than an equivalent style
rule that does not carry the "!important" keyword. When equivalent style
rules in an author and user style sheet both carry the "!important" keyword,
the user's style rule takes precedence.
In CSS1, an author "!important" declaration has precedence over a
user "!important" declaration. This was changed in CSS2 to its current behavior.
Setting a shorthand property to be "!important" sets all of its
sub-properties to "!important" as well, whether explicitly specified or
not (eg: setting the 'font' property for a selector as "!important" is
the same as setting the 'font-style', 'font-variant', 'font-weight',
'font-size, 'line-height', and 'font-family' properties as "!important.")
Browser Peculiarities
Internet Explorer
4.0:
- If an extra asterisk character ("*") is placed just before
the end of a comment (eg: using "**/" instead of "*/"), the
comment is not terminated, and valid style declarations that
follow are also treated as comments.
Netscape
4.x+:
- Reported Elsewhere: Some cases of using the "!important" keyword
can cause the entire style declaration to be ignored (noted
situation: when the "!important" statement immediately follows
a style declaration without spaces between them.)