code: private AbsAxis parseAbbrevForwardStep() {
  
          AbsAxis axis;
          boolean isAttribute;
  
          if (is(TokenType.AT, true) || mToken.getContent().equals("attribute")
              || mToken.getContent().equals("schema-attribute")) {
              // in case of .../attribute(..), or .../schema-attribute() the
              // default
              // axis
              // is the attribute axis
              axis = new AttributeAxis(getTransaction());
              isAttribute = true;
          } else {
              // default axis is the child axis
              axis = new ChildAxis(getTransaction());
              isAttribute = false;
          }
  
          final AbsFilter filter = parseNodeTest(isAttribute);
  
          return new FilterAxis(axis, mRTX, filter);
      }
docs: Parses the the rule AbrevForwardStep according to the following
  production rule:
  <p>
  [31] AbbrevForwardStep ::= "@"? NodeTest .
  </p>
  
  @return FilterAxis