code: public ExtensionManager registerUserDefinedParsers(String dialect, IParserFactory... parsers) {
          engine.dialectManager().registerExternalParsers(dialect, parsers);
          return this;
      }
docs: Register a special case parser to a dialect
  <p/>
  <p>for example, the play-rythm plugin might want to register a special case parser to
  process something like @{Controller.actionMethod()} or &{'MSG_ID'} etc to "japid"
  and "play-groovy" dialects
  
  @param dialect
  @param parsers