Eric A. Meyer - CSS: The Definitive Guide, 3rd Edition

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• An asterisk (*) indicates that the preceding value or bracketed group is repeated zero or more times. Thus, bucket* means that the word bucket can be used any number of times, including zero. There is no upper limit defined on the number of times it can be used.

• A plus (+) indicates that the preceding value or bracketed group is repeated one or more times. Thus, mop+ means that the word mop must be used at least once, and potentially many more times.

• A question mark (?) indicates that the preceding value or bracketed group is optional. For example, [pine tree]? means that the words pine tree need not be used (although they must appear in that exact order if they are used).

• A pair of numbers in curly braces ({M,N}) indicates that the preceding value or bracketed group is repeated at least M and at most N times. For example, ha{1,3} means that there can be one, two, or three instances of the word ha.

At least one of the three words must be used, and they can be used in any order. For example, give liberty, give me, liberty me give, and give me liberty are all valid.

Either the word I or am may be used, but not both, and use of either is optional. In addition, either the or walrus, or both, must follow in any order. Thus, you could construct I the walrus, am walrus the, am the, I walrus, walrus the, and so forth.

One or more instances of koo must be followed by ka-choo. Therefore, koo koo ka-choo, koo koo koo ka-choo, and koo ka-choo are all legal. The number of koos is potentially infinite, although there are bound to be implementation-specific limits.

This is the all-purpose web designer's opinion expresser. This example can be interpreted as I love Netscape, I really love Microsoft, and similar expressions. Anywhere from zero to four reallys may be used. You also get to pick between love and hate, even though only love was shown in this example.

This is a potentially long and complicated expression. One possible result would be Alpha, Cray, and Delphi. The comma is placed because of its position within the nested bracket groups.

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