code: function mouseDown_(ev) {
      var e=ev||event;
      setCursor_(true);
      event_.trigger(me, "mousedown", e);
      if (src.style.position !== "absolute") {
        src.style.position = "absolute";
        return;
      }
      formerMouseX_ = e.pageX||(e.clientX+document.body.scrollLeft+document.documentElement.scrollLeft);
      formerMouseY_ = e.pageY||(e.clientY+document.body.scrollTop+document.documentElement.scrollTop);
      originalX_ = src.offsetLeft;
      originalY_ = src.offsetTop;
      formerX_ = originalX_;
      formerY_ = originalY_;
      mouseMoveEvent_ = event_.addDomListener(target_, "mousemove", mouseMove_);
      if (src.setCapture) {
        src.setCapture();
      }
      if (e.preventDefault) {
        e.preventDefault();
        e.stopPropagation();
      } else {
        e.cancelBubble=true;
        e.returnValue=false;
      }
      moving_ = true;
      event_.trigger(me, "dragstart", {mouseX: formerMouseX_, mouseY: formerMouseY_, startLeft: originalX_, startTop: originalY_, event:e});
    }
docs: Handles the mousedown event.
  @param {event} ev The event data sent by the browser.
  @private