code: Rule XcomTextblock() {
  		return Sequence(String("begintext"), OptionalS(TextblockParam()), Eol(),
  				ZeroOrMoreS(SequenceS(OptionalS(String("%%")), TexText(), Eol())),
  				String("%%endtext")
  				).label(XcomTextblock);
  	}
docs: xcom-textblock ::= "begintext" [textblock-param] eol *(["%%"] tex-text) "%%endtext"