code: public function setReferencePattern(
          /*# string */ $start,
          /*# string */ $end
      ) {
          $this->ref_start = $start;
          $this->ref_end = $end;
  
          // build pattern on the fly
          $s = preg_quote($start);
          $e = preg_quote($end);
          $this->ref_pattern = sprintf(
              "~(%s((?:(?!%s|%s).)+?)%s)~",
              $s,
              $s,
              $e,
              $e
          );
      }
docs: {@inheritDoc}