code: Rule FieldMeter() {
  		return Sequence(String("M:"),
  				ZeroOrMore(WSP()).suppressNode(),
  				OptionalS(TimeSignature()), HeaderEol()).label(FieldMeter);
  	}
docs: field-meter ::= %x4D.3A *WSP time-signature header-eol<p>
  <tt>M:</tt>