update( element, out ) { 	/* eslint-enable no-unused-vars */

		//console.log( "BoxLayouter update", element.name );
		// reset
		this._childrenPos = {};

		for ( const uiBoxElement of element._children._boxes ) {

			//console.log( uiBoxElement._position._value )
			if( uiBoxElement._position._value === 'static' ) {

				// bind position
				this._childrenPos[ uiBoxElement.id ] = uiBoxElement.position;

			}

		}

	}
Updated when :
	- New child added
	- Child removed
	- Child position changed
	- Child visibility changed
	- ...?
	@override