2008 March 26th Wednesday (三月 二十六日 水曜日）

Character classes.  A POSIX character class consists of keywords bracketed by [: and :].  The keywords describe different classes of characters such as
alphabetic characters, control characters, and so on.

  Collating symbols.  A collating symbol is a multicharacter sequence that should be treated as a unit.  It consists of the characters bracketed by [. and .].

  Equivalence classes.  An equivalence class lists a set of characters that should be considered equivalent, such as e and e. It consists of a named element
from the locale, bracketed by [= and =].