function constructSelectEvent(nativeEvent, nativeEventTarget) {
	  // Ensure we have the right element, and that the user is not dragging a
	  // selection (this matches native `select` event behavior). In HTML5, select
	  // fires only on input and textarea thus if there's no focused element we
	  // won't dispatch.
	  if (mouseDown || activeElement == null || activeElement !== getActiveElement()) {
	    return null;
	  }

	  // Only fire when selection has actually changed.
	  var currentSelection = getSelection(activeElement);
	  if (!lastSelection || !shallowEqual(lastSelection, currentSelection)) {
	    lastSelection = currentSelection;

	    var syntheticEvent = SyntheticEvent.getPooled(eventTypes.select, activeElementInst, nativeEvent, nativeEventTarget);

	    syntheticEvent.type = 'select';
	    syntheticEvent.target = activeElement;

	    EventPropagators.accumulateTwoPhaseDispatches(syntheticEvent);

	    return syntheticEvent;
	  }

	  return null;
	}
Poll selection to see whether it's changed.

@param {object} nativeEvent
@return {?SyntheticEvent}