code: public function addEntryPattern($pattern, $mode, $new_mode)
      {
          if (! isset($this->regexes[$mode])) {
              $this->regexes[$mode] = new ParallelRegex($this->case);
          }
          $this->regexes[$mode]->addPattern($pattern, $new_mode);
          if (! isset($this->mode_handlers[$new_mode])) {
              $this->mode_handlers[$new_mode] = $new_mode;
          }
      }
docs: Adds a pattern that will enter a new parsing mode.
  Useful for entering parenthesis, strings, tags, etc.
  
  @param string $pattern      Perl style regex, but ( and ) lose the usual meaning.
  @param string $mode         Should only apply this pattern when dealing with this type of
  input.
  @param string $new_mode     Change parsing to this new nested mode.