code: @SuppressWarnings("unchecked")
  	private <T> T execOperator(Element element, Object scope, Meta meta, Format... format) throws IOException {
  		Operator operator = factory.geInstance(meta.opcode);
  		return (T) operator.exec(element, scope, meta.operand, format.length == 1 ? format[0] : null);
  	}
docs: Helper method for operator execution.
  
  @param element
  @param scope
  @param meta
  @return operator specific value, cast to any type or null.
  @throws IOException if underlying writer fails to write.