Select All Objects beneath a Target Object.
In the attached image, I wanted to select and delete all of the boxes that sat beneath the red stroke. In order to do it, I had to duplicate the red stroke, convert it to an outline, select all of the boxes, Unite them with the outlined red stroke and then delete the boxes that were fused with the stroke. Doing this results in the other boxes losing their original color.
Could there be a variation on the selection tool that detects all of the objects that are underneath a target object (in this case the red stroke)?
Egor Chistyakov commented
Meanwhile, continue the trick one step further: grab you outlined line, copy it, undo the Unite operation, paste in place( on front) your united line+rectangles over original art (but hide the live stroke one), select all, execute Merge command, delete the new united part again. This can be mostly automated with actions too.