function triggerMouseEvent(eventName, event, targetElement) {

    // i.e. element.mousedown...
    var localEventName = bindings[eventName];

    if (!localEventName) {
      throw new Error('unmapped DOM event name <' + eventName + '>');
    }

    return fire(localEventName, event, targetElement);
  }
Trigger an interaction event (based on a native dom event)
on the target shape or connection.

@param {string} eventName the name of the triggered DOM event
@param {MouseEvent|TouchEvent} event
@param {Element} targetElement