A handler for <forEach> that supports rtexprvalue-based attributes.
this.beginSpecified = true; this.begin = begin; validateBegin();
this.endSpecified = true; this.end = end; validateEnd();
// for null items, simulate an empty list if (o == null) rawItems = new ArrayList(); else rawItems = o;
this.stepSpecified = true; this.step = step; validateStep();