Appendices-Terms-Declaration sequence

Full details are given in the topic on [Commands]. But in brief:

Possible sequence	Possible child sequences	What it means
\keyword\		Declares a contextual keyword.
[sequence]	Any other sequence	Declares an optional child sequence.
(sequence1 | sequence2) Any other required sequence	Allows the caller to use either of two sequences, but not both. The selected sequence can’t be repeated.
{sequence1 | sequence2}	Any other sequence	The caller must use each sequence, but those sequences can appear in any order.
(sequence)...identifier	Any other sequence	Declares a sequence which can be repeated as often as needed. The specified identifier becomes an array with details.

You can make parentheses, brackets, and braces keywords. However, the compiler will require matching sets to present in both the declaration and the call of your procedure. So if it sees “\(\”, it will then require “\)\” later on.

Some symbols can’t be made into keywords. Those are both types of quotes, the backslash, and the period. If the parser sees a comma in your syntax, it will treat that as \,\ that may or may not be required depending on the context.