"I think Oleg was using "mix" in the sense of "confuse" - rather than "combine?""

Yes, I understood that.

My point was that the original confusion was between different methods of doing ISP rather than between 'SPI' (an interface) and 'ISP' (a method). I'm a bit sore about this one because I've mixed them up myself on this forum and had it pointed out to me somewhat tersely. TLAs should be abolished.