Cascading Style Sheets, Level 2 - World Wide Web Consortium

4.1.6 Blocks
A block starts with a left curly brace ({) and ends with the matching right curly
brace (}). In between there may be any characters, except that parentheses (( )),
brackets ([ ]) and braces ({ }) must always occur in matching pairs and may be
nested. Single (’) and double quotes (") must also occur in matching pairs, and
characters between them are parsed as a string. See Tokenization [p. 35] above
for the definition of a string.
Illegal example(s):
Here is an example of a block. Note that the right brace between the double
quotes does not match the opening brace of the block, and that the second
single quote is an escaped character [p. 38] , and thus doesn’t match the first
single quote:
{ causta: "}" + ({7} * ’\’’) }
Note that the above rule is not valid CSS2, but it is still a block as defined
above.
4.1.7 Rule sets, declaration blocks, and selectors
A rule set (also called "rule") consists of a selector followed by a declaration
block.
A declaration-block (also called a {}-block in the following text) starts with a left
curly brace ({) and ends with the matching right curly brace (}). In between there
must be a list of zero or more semicolon-separated (;) declarations.
The selector (see also the section on selectors [p. 53] ) consists of everything
up to (but not including) the first left curly brace ({). A selector always goes
together with a {}-block. When a user agent can’t parse the selector (i.e., it is not
valid CSS2), it must ignore [p. 42] the {}-block as well.
CSS2 gives a special meaning to the comma (,) in selectors. However, since it
is not known if the comma may acquire other meanings in future versions of
CSS, the whole statement should be ignored [p. 42] if there is an error anywhere
in the selector, even though the rest of the selector may look reasonable in
CSS2.
Illegal example(s):
For example, since the "&" is not a valid token in a CSS2 selector, a CSS2
user agent must ignore [p. 42] the whole second line, and not set the color of H3
to red:
H1, H2 {color: green }
H3, H4 & H5 {color: red }
H6 {color: black }
Example(s):
Here is a more complex example. The first two pairs of curly braces are inside
a string, and do not mark the end of the selector. This is a valid CSS2 statement.
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