In the case of nested interrupts, does the "ISR == background" view mean there are multiple backgrounds? Or is the highest-priority IRQ the background, and the rest a part of IRQs the foreground? Doesn't make sense to me - but it's nevertheless a sincere question. ;-)
Now I'll go back to not using those two words.
Even if they are not nested, multiple ISRs ( e.g., CAN, UART, Timer, ...) exist in many (most?) systems. So whether you're an "ISR = 'f' word" or "ISR = 'b' word" proponent, what do you do?
~Dave~