Just a note: I believe that the original historical meaning of "hotspots" is to mark a pixel in cursor image where the actual click operation takes place (e.g. the tip of the arrow). Hotspot1 marks left click Hotspot2 is does the same for right click. You can try this easily just by assigning an image with hotspots as a mouse pointer.
I think that all the usage in chameleon is just clever reusing the existing feature to completely different purpose
Best regards,
Honza
Actually, hotspot1 is common. However, hotspot2 is U++'s unique feature. In fact, in the beginning there was an idea to use reuse hotspot1 for chameleon and what is now hotspot2 was resolved by diagonal symmetry. But using hotspot2 is definitely better solution.
BTW, inverse placement of hotspots (in either vertical or horizontal sense) leads to some more funny options (it means "repeat"). But while it seemed like a good idea back then, it was never used AFAIK.