code: Rule IfieldComposer() {
  		return Sequence(String("[C:"),
  				ZeroOrMore(WSP()).suppressNode(),
  				TexTextIfield(),
  				String("]"))
  			.label(IfieldComposer);
  	}
docs: ifield-composer ::= %5B.%43.%3A *WSP tex-text-ifield %5D<p>
  <tt>[C:..]</tt>