Regular expression metacharacters

The characters that mean something other than themselves inside a pattern. The group is small because only the POSIX core is catalogued: later dialects extend and diverge from it, and a record describing a construct as universal when PCRE and ECMAScript disagree about it would be wrong. Two members carry more than one job apiece, and the records say so — the caret anchors at the front of a pattern and negates inside a bracket, and nothing but position distinguishes them.