Returns a valid regular expression which will match string, ignoring case. This
expression is string with
each character converted to a bracket expression; this
bracket expression contains that character's uppercase and
lowercase form if applicable, otherwise it contains the
original character twice.
[Ff][Oo][Oo] [Bb][Aa][Rr] |
This can be used to achieve case insensitive pattern
matching in products which support only case sensitive
regular expressions.