def drag_contents_to(how, what)
      assert_exists # assert_enabled?
      val = self.value
      self.value = ''
      @container.text_field(how, what).append(val)
    end
def drag_contents_to(how, what)
      assert_exists # assert_enabled?
      val = self.value
      self.value = ''
      @container.text_field(how, what).append(val)
    end
This bascially just moves the text to the other text field using TextField#append
 TODO: check if HtmlUnit supports some kind of dragging.