code: private void parsePredicate() throws TTXPathException {
  
          consume(TokenType.OPEN_SQP, true);
  
          mPipeBuilder.addExpressionSingle();
  
          parseExpression();
  
          consume(TokenType.CLOSE_SQP, true);
  
          mPipeBuilder.addPredicate(getTransaction());
      }
docs: Parses the the rule Predicate according to the following production rule:
  <p>
  [40] Predicate ::= "[" Expr "]" .
  </p>
  <p>
  The whole predicate expression is build as a separate expression chain and is then inserted to the main
  expression chain by a predicate filter.
  </p>
  
  @throws TTXPathException