code: Rule IfieldHistory() {
  		return Sequence(String("[H:"),
  				ZeroOrMore(WSP()).suppressNode(),
  				TexTextIfield(),
  				String("]"))
  			.label(IfieldHistory);
  	}
docs: ifield-history ::= %5B.%48.%3A *WSP tex-text-ifield %5D<p>
  <tt>[H:..]</tt>