code: Rule IfieldBook() {
  		return Sequence(String("[B:"),
  				ZeroOrMore(WSP()).suppressNode(),
  				TexTextIfield(),
  				String("]"))
  			.label(IfieldBook);
  	}
docs: ifield-book ::= %5B.%42.%3A *WSP tex-text-ifield %5D<p>
  <tt>[B:..]</tt>