getZIndexBelowPopups() {
			const aOpenPopups = getPopups();
			let iLowestPopupZIndex;

			if (aOpenPopups.length > 0) {
				iLowestPopupZIndex = Math.min.apply(null, getZIndexFromPopups(aOpenPopups));
			}

			// if no open popups
			if (!Util.isInteger(iLowestPopupZIndex)) {
				return Popup.getNextZIndex();
			}

			// get the minimum possible z-index
			return this._getNextMinZIndex(iLowestPopupZIndex);
		}
Calculates the z-index value below open popups.
If there are no open popups it returns the value from sap.ui.core.Popup.getNextZIndex()
@returns {int} z-index below open popups
@public