code: Rule FieldVoice() {
  		return Sequence(String("V:"),
  				ZeroOrMore(WSP()).suppressNode(),
  				Voice(), HeaderEol()).label(FieldVoice);
  	}
docs: field-voice ::= %x56.3A *WSP voice header-eol<p>
  <tt>V:</tt>
  
  options should be better defined