List Operators

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List Operators (`[' ... `]' and `[^' ... `]')
=============================================

  "Lists", also called "bracket expressions", are a set of one or more
items.  An "item" is a character, a character class expression, or a
range expression.  The syntax bits affect which kinds of items you can
put in a list.  We explain the last two items in subsections below.
Empty lists are invalid.

  A "matching list" matches a single character represented by one of
the list items.  You form a matching list by enclosing one or more items
within an "open-matching-list operator" (represented by `[') and a
"close-list operator" (represented by `]').

  For example, `[ab]' matches either `a' or `b'.  `[ad]*' matches the
empty string and any string composed of just `a's and `d's in any
order.  Regex considers invalid a regular expression with a `[' but no
matching `]'.

  "Nonmatching lists" are similar to matching lists except that they
match a single character *not* represented by one of the list items.
You use an "open-nonmatching-list operator" (represented by `[^'(1))
instead of an open-matching-list operator to start a nonmatching list.

  For example, `[^ab]' matches any character except `a' or `b'.

  If the `posix_newline' field in the pattern buffer (*note GNU Pattern
Buffers::. is set, then nonmatching lists do not match a newline.

  Most characters lose any special meaning inside a list.  The special
characters inside a list follow.

`]'
     ends the list if it's not the first list item.  So, if you want to
     make the `]' character a list item, you must put it first.

`\'
     quotes the next character if the syntax bit
     `RE_BACKSLASH_ESCAPE_IN_LISTS' is set.

`[:'
     represents the open-character-class operator (*note Character
     Class Operators::.) if the syntax bit `RE_CHAR_CLASSES' is set and
     what follows is a valid character class expression.

`:]'
     represents the close-character-class operator if the syntax bit
     `RE_CHAR_CLASSES' is set and what precedes it is an
     open-character-class operator followed by a valid character class
     name.

`-'
     represents the range operator (see Range Operator.) if it's
     not first or last in a list or the ending point of a range.

All other characters are ordinary.  For example, `[.*]' matches `.' and
`*'.
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