Regular Expressions 1: Vocabulary

Terms used to describe regular expressions,
and the basic buiding blocks.
Ref.: Mastering Regular Expressions. Jeffrey E. F. Friedl, O'Reilly 1997
Also try Regular Expressions 2: Exercises
(http://www.quia.com/mc/71732.html)
Convention: "..." is not part of a regex, but meant to indicate the presence of some item (subexpression).