var DWM_navBar = null;
var DWM_navBarTop = 0;
var DWM_navBarFx = null;

function DWM_moveNavScroll() {

	var scroll = Window.getScroll();
	var newTop = scroll.y - 300;
	if ( newTop < 0 ) {
		newTop = 0;
	}
	if ( newTop != DWM_navBarTop ) {
      DWM_navBarFx.start( newTop );
	  DWM_navBarTop = newTop;
	}
}

function DWM_initNavScroll() {

	DWM_navBar = $( 'nav' );
	if ( DWM_navBar ) {
		DWM_navBarFx = new Fx.Tween( DWM_navBar, {
			'unit': 'px',
			'link': 'cancel',
			'duration': 100,
			'transition': 'linear',
			'property': 'top'
		} );
	}

    ( function() { DWM_moveNavScroll(); } ).periodical( 300 );
}

window.addEvent( 'domready', DWM_initNavScroll );