Presently when drawing rectangles, the drag will snap to major metrics such as the baseline, cap height, etc. I would also find it useful if they would also snap to the beginning height of all other alignment zones (e.g. one set up for a small-caps height that differs from the l/c x-height).
…also would be useful to see diamonds on the nodes when the height of it is right on the beginning of any alignment zone, like we see with the baseline/cap height/etc.