fnzIndex = function( zIndex ) {
			if ( zIndex !== undefined ) {
				return this.css( "zIndex", zIndex );
			}

			if ( this.length ) {
				var elem = jQuery( this[ 0 ] ), position, value;
				while ( elem.length && elem[ 0 ] !== document ) {
					// Ignore z-index if position is set to a value where z-index is ignored by the browser
					// This makes behavior of this function consistent across browsers
					// WebKit always returns auto if the element is positioned
					position = elem.css( "position" );
					if ( position === "absolute" || position === "relative" || position === "fixed" ) {
						// we ignore the case of nested elements with an explicit value of 0
						// <div style="z-index: -10;"><div style="z-index: 0;"></div></div>
						value = parseInt( elem.css( "zIndex" ));
						if ( !isNaN( value ) && value !== 0 ) {
							return value;
						}
					}
					elem = elem.parent();
				}
			}

			return 0;
		}
Get (if no zIndex parameter is given) or set the z-index for an element.

@param {int} [zIndex] The z-index to set
@returns {jQuery | number} The z-index
@public
@name jQuery#zIndex
@function
@requires module:sap/ui/dom/jquery/zIndex