code: public void addChildValueSelect(final AbstractValueSelect _valueSelect)
          throws EFapsException
      {
          if (this.child == null) {
              this.child = _valueSelect;
              _valueSelect.setParentValueSelect(this);
          } else {
              this.child.addChildValueSelect(_valueSelect);
          }
      }
docs: Method adds an AbstractValueSelect as a child of this chain of
  AbstractValueSelect.
  
  @param _valueSelect AbstractValueSelect to be added as child
  @throws EFapsException on error