code: private void parseForwardStep() throws TTXPathException {
  
          AbsAxis axis;
          AbsFilter filter;
          if (isForwardAxis()) {
              axis = parseForwardAxis();
              filter = parseNodeTest(axis.getClass() == AttributeAxis.class);
  
              mPipeBuilder.addStep(axis, filter);
          } else {
              axis = parseAbbrevForwardStep();
  
              mPipeBuilder.addStep(axis);
          }
      }
docs: Parses the the rule ForwardStep according to the following production
  rule:
  <p>
  [29] ForwardStep ::= (ForwardAxis NodeTest) | AbbrevForwardStep .
  </p>
  
  @throws TTXPathException