UI.draggable - limits/boundaries

Would be nice to have limits/boundaries for draggable elements. Currently it can be limited by a parent element and by x- or y-axis.

Example for implementation:

jQuery('#drag').draggable({
  limit: {top: 50, left: 100, bottom: 200, right: 200}
});

jQuery('#dragHorizontal').draggable({
  axis : 'x',
  limit: {left: 100, right: 400}
});

I don't know if top, left, bottom and right would be best to set the boundaries, an other idea is to use x1, y1, x2 and y2.