Same as [method@Gtk.
TextIter.forward_search], but moves backward.
match_end will never be set to a `GtkTextIter` located after this, even if there is a possible
match_start before or at this.
a `GtkTextIter` where the search begins
bitmask of flags affecting the search
return location for start of match
return location for end of match
location of last possible
whether a match was found