code: public void addCastableExpr(final INodeReadTrx mTransaction, final SingleType mSingleType) {
  
          assert getPipeStack().size() >= 1;
  
          final AbsAxis candidate = getPipeStack().pop().getExpr();
  
          final AbsAxis axis = new CastableExpr(mTransaction, candidate, mSingleType);
          if (getPipeStack().empty() || getExpression().getSize() != 0) {
              addExpressionSingle();
          }
          getExpression().add(axis);
  
      }
docs: Adds a castable expression to the pipeline.
  
  @param mTransaction
  Transaction to operate with.
  @param mSingleType
  single type the context item will be casted to.