Search backward from point for match for regular expression REGEXP.
Set point to the beginning of the match, and return point.
The match found is the one starting last in the buffer
and yet ending before the origin of the search.
An optional second argument bounds the search; it is a buffer position.
The match found must start at or after that position.
Optional third argument, if t, means if fail just return nil (no error).
If not nil and not t, move to limit of search and return nil.
Optional fourth argument is repeat count--search for successive occurrences.
Search case-sensitivity is determined by the value of the variable
`case-fold-search', which see.
See also the functions `match-beginning', `match-end', `match-string',
and `replace-match'. (fn REGEXP &optional BOUND NOERROR COUNT)