Arguments are generally identified with a prefix character.

In the UNIX world, this character is almost universally the dash or hyphen, although plus signs and double dashes have become more common in recent years.

In the DOS/Windows world, forward slashes are somewhat more common than dashes.

The DocBook processing expectations on this point are intentionally vague. In some environments it may be most convenient to generate these characters automatically; in other environments it may be more convenient to insert them literally in the content.

Whichever processing model you choose, note that this will be an interchange issue if you share documents with other users (see Appendix D, Interchanging DocBook Documents).

Brackets are used to distinguish between optional, required, or plain arguments. Usually square brackets are placed around optional arguments, [-g], and curly brackets are placed around required arguments, {-g}. Plain arguments are required, but are not decorated with brackets.

Repeatable arguments are followed by an ellipsis.

Multiple arguments within a group are considered exclusive and are separated by vertical bars.

Groups, like arguments, may be optional, required, or plain and may or may not repeat. The same brackets and ellipses that are used to indicate these characteristics on arguments are used on groups.

Arguments and groups may nest more or less arbitrarily.

The element is formatted as a displayed block. The processing system is free to introduce line breaks where required, but the sbr element may be introduced by the author to provide an explicit break location.