code: Rule UnusedField() {
  		//TODO remove s:symbol-line
  		return Sequence(
  				AnyOf("EJYabcdefghijklnopqrstvxyz")
  				/*FirstOf('E', 'I', 'J', 'Y',
  						CharRange('a', 'l'),
  						CharRange('n', 't'),
  						'v', 'x', 'y', 'z')*/
  					.label("UnusedFieldLetter").suppressSubnodes(),
  				String(":"),
  				ZeroOrMore(WSP()).suppressNode(),
  				TexText(), HeaderEol()).label(UnusedField);
  	}
docs: ignore - but for backward and forward compatibility
  
  unused-field ::= (%x45 / %x49 / %4A / %59 / %61-6c / %6e-%74 / %76 / %78-7A) %3A *(WSP / VCHAR) eol<p>
  <tt>E: I: J: Y: a:-l: n:-t: v: x: y: z:</tt>