regular expression - an expression that specifies a set of strings of characters.

regular expression match - A member of the set of strings determined by a regular expression is said to be matched by the regular expression.

collating symbol - symbol of the form [.xxx.] where xxx is a collating element.

collating element - a single character or an N-to-1 collation unit.

X/Open and POSIX.1 have different sets of regular expression handling functions to do the same thing.

character class expression - expression of the form [:class_name:] where class_name is the name of a character class.

primary equivalence class expression - expression of the form [=x=] where x is a member of the desired equivalence class.

A period '.' will never match an N-to-1 collation unit.

range expression - expression of the form [x-y] where x and y are characters.

Range expressions are discouraged.

The syntax and semantics of the following regular expression constructs are not affected by I18N: anchoring, subexpressions, backreference expressions \n, interval expressions {m}, matching and nonmatching list expressions.