In the PGF/TikZ manual, sometimes I see the option
right of=somenode instead of
right=of somenode. They look very similar, but the effects are different. The distance between nodes positioned with the latter option is boundary-to-boundary, as stated in the manual. However, with the first option, it seems that the distance is shorter. I couldn't find any explanation of the first option in the manual.
My question is: what is the difference between the two options? Is there any explanation in the manual that I missed?