Regex
Regex
| or \|)
If the syntax bit RE_LIMITED_OPS is set, then Regex doesn't
recognize this operator. Otherwise, if the syntax bit
RE_NO_BK_VBAR is set, then | represents this operator;
otherwise, \| does.
Alternatives match one of a choice of regular expressions:
if you put the character(s) representing the alternation operator between
any two regular expressions a and b, the result matches
the union of the strings that a and b match. For
example, supposing that | is the alternation operator, then
foo|bar|quux would match any of foo, bar or
quux.
The alternation operator operates on the largest possible
surrounding regular expressions. (Put another way, it has the lowest
precedence of any regular expression operator.)
Thus, the only way you can
delimit its arguments is to use grouping. For example, if ( and
) are the open and close-group operators, then fo(o|b)ar
would match either fooar or fobar. (foo|bar would
match foo or bar.)
The matcher usually tries all combinations of alternatives so as to
match the longest possible string. For example, when matching
(fooq|foo)*(qbarquux|bar) against fooqbarquux, it cannot
take, say, the first (``depth-first'') combination it could match, since
then it would be content to match just fooqbar.