var maxY:Number = 0;
var minY:Number = Math.min(0, stage.stageHeight - content.height);
var _startY:Number;
var _startMouseY:Number;
addEventListener(MouseEvent.MOUSE_DOWN, mouseDownHandler);

function mouseDownHandler(event:MouseEvent):void
{
    _startY = content.y;
    _startMouseY = mouseY;
    stage.addEventListener(MouseEvent.MOUSE_MOVE, stage_mouseMoveHandler, false, 0, true);
    stage.addEventListener(MouseEvent.MOUSE_UP, stage_mouseUpHandler, false, 0, true);
}

function stage_mouseMoveHandler(event:MouseEvent):void
{
    var offsetY:Number = mouseY - _startMouseY;
    content.y = Math.max(Math.min(maxY, _startY + offsetY), minY);
}

function stage_mouseUpHandler(event:MouseEvent):void
{
    stage.removeEventListener(MouseEvent.MOUSE_MOVE, stage_mouseMoveHandler);
    stage.removeEventListener(MouseEvent.MOUSE_UP, stage_mouseUpHandler);
}