Search backward from point for STRING.
Set point to the beginning of the occurrence found, and return point.
An optional second argument bounds the search; it is a buffer position.
The match found must not extend before that position.
Optional third argument, if t, means if fail just return nil (no error).
If not nil and not t, position at limit of search and return nil.
Optional fourth argument COUNT, if non-nil, means to search for COUNT
successive occurrences. If COUNT is negative, search forward,
instead of backward, for -COUNT 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' and `replace-match'.
(fn STRING &optional BOUND NOERROR COUNT)