(regex target-string &key start end sharedp) &body body)
|Function: Executes BODY with the variables in VAR-LIST bound to the corresponding register groups after TARGET-STRING has been matched against REGEX, i.e. each variable is either bound to a string or to NIL. If there is no match, BODY is _not_ executed. For each element of VAR-LIST which is NIL there's no binding to the corresponding register group. The number of variables in VAR-LIST must not be greater than the number of register groups. If SHAREDP is true, the substrings may share structure with TARGET-STRING.