code: public void setOnMouseDown(String onMouseDown) {
          _imageState.registerAttribute(AbstractHtmlState.ATTR_JAVASCRIPT, HtmlConstants.ONMOUSEDOWN, onMouseDown);
      }
docs: Sets the onMouseDown JavaScript event on the image tag.
  
  @param onMouseDown the onMouseDown event.
  @jsptagref.attributedescription The onMouseDown JavaScript event on the image tag.
  @jsptagref.attributesyntaxvalue <i>string_onMouseDown</i>
  @netui:attribute required="false" rtexprvalue="true" description="The onMouseDown JavaScript event on the image tag."