Searches TARGET-STRING from START to END and tries
to match REGEX. On success returns four values - the start of the
match, the end of the match, and two arrays denoting the beginnings
and ends of register matches. On failure returns NIL. REGEX can be a
string which will be parsed according to Perl syntax, a parse tree, or
a pre-compiled scanner created by CREATE-SCANNER. TARGET-STRING will
be coerced to a simple string if it isn't one already. The
REAL-START-POS parameter should be ignored - it exists only for
internal purposes.