function fnCheckAggregationOverlayVisibility(oAggregationOverlay, oParentElement) {
			// this function can get called on overlay registration, when there are no overlays in dom yet. In this case, DOMUtil.isVisible is always false.
			var oAggregationOverlayDomRef = oAggregationOverlay.getDomRef();
			var bAggregationOverlayVisibility = DOMUtil.isVisible(oAggregationOverlayDomRef);

			// if there is no aggregation overlay domRef available the further check for domRef of the corresponding element is not required
			if (!oAggregationOverlayDomRef) {
				return bAggregationOverlayVisibility;
			}
			// additional check for corresponding element DomRef visibiltiy required for target zone checks during navigation mode.
			// during navigation mode the domRef of valid overlays is given and the offsetWidth is 0. Therefor we need to check the visibility of the corresponding element additionally
			var oParentElementDomRef = oParentElement && oParentElement.getDomRef && oParentElement.getDomRef();
			var bAggregationElementVisibility = oParentElementDomRef ? DOMUtil.isVisible(oParentElementDomRef) : true;
			return bAggregationOverlayVisibility || bAggregationElementVisibility;
		}
Checks if an aggregation is valid for an element being moved

@param {sap.ui.dt.AggregationOverlay} oAggregationOverlay - Aggregation overlay to be checked for target zone
@param {sap.ui.dt.ElementOverlay} oMovedOverlay - Overlay being moved
@param {boolean} bOverlayNotInDom - Flag defining if overlay is not in DOM
@returns {Promise.<boolean>} Resolved promise with <code>true</code> if the aggregation overlay is a valid target zone for the overlay