A '''metacharacter''' is a term often used in relation to various kinds of [regular expressions] to mean a ''short-cut'' name for something else. In general, it refers to a character that is involved in the processing of the message itself and not of the content of the message, taking “message” in a generalised sense. For example, the syntax rules described in the Tcl.n [dodecalogue] describes Tcl's metacharacters; the remaining manual pages describe the content of the “messages”, which in Tcl are command invocations. (Some of these recursively use the basic Tcl syntax — e.g., [if], [while], [proc] — but which do and which don't is a feature of the particular commands.) <> Glossary