jquery-svg | jQuery plugin to apply css styles | Animation library

This is really only a partial answer, as I can show you how to accomplish your goal in simple situations, but not in all the scenarios you proposed.

A simplistic solution would be to use svgSvgElement.getIntersectionList. The code below demonstrates this. It shows how to determine which of three colored triangles are "hit" by a selection rectangle. Note, however, that it determines not which elements overlap the selection rectangle but which element bounding boxes overlap the selection rectangle. Thus, the blue triangle below is considered to overlap as expected and the red triangle is considered to not overlap as expected, but the green triangle is considered to overlap not because the triangle itself does but because the dotted green rectangle around it does. To actually determine which shape itself overlaps the rectangle is more complicated and has been the source of much hair-pulling since the dawn of time.