code: private void startMouseSliding(Event event) {
  
          if (!m_slidingMouse) {
              m_slidingMouse = true;
              DOM.setCapture(getElement());
              m_mouseSlidingStartY = event.getClientY();
              m_mouseSlidingStartValue = m_currentValue;
              CmsDebugLog.getInstance().printLine(
                  "Mouse sliding started with clientY: "
                      + m_mouseSlidingStartY
                      + " and start value: "
                      + m_mouseSlidingStartValue
                      + " and a max value of "
                      + getMaximumVerticalScrollPosition());
          }
      }
docs: Starts the mouse sliding.<p>
  
  @param event the mouse event