I have googled around and as yet have found no answer (or none simple enough for me to understand) to this question, so will risk revealing my ignorance yet again.
I'm used to working with Leonardos and Unos. If you look up, say, the Leonardo spec on arduino.cc, you find that i2c (Wire) is implemented on pins 2 and 3 (SDA and SCL). If you look up the Uno, you find that the i2c pins are A4 and A5. On both these devices, the relevant pins are also ganged to a couple of sockets just above AREF, labelled SDA and SCL; but you can connect directly to pins 2 and 3, or A4 and A5, as the case may be.
I've got used to this and it makes sense to me. When I use i2c I know that even though I might only plug bus wires into the sockets labelled SDA and SCL, I can't use the "real" pins (2 and 3, on a Leo) for any other purpose because they are busy doing i2c. On a Leo, D2 and D3 are used up if you are running the Wire library. So far so good.
Now, in preparation for playing with a Zero M0 clone I ordered, I'm trying to figure out which pins are used for i2c (which pins can I not use for other purposes if I have Wire loaded). I see that above AREF there are the usual 2 sockets labelled SDA and SCL, but I'm having a hard time figuring out which digital or analog pins are the "real" SDA and SCL. This page
reveals this info for many duino models, but not the Zero.
I ran across a writeup at Adafruit about using multiple i2c interfaces (possible because of multiple "serial devices" implemented on the Atmel chip) but it quickly exceeded my experience level and confused me further. Is there a simple answer? I found a circuit diagram of the Zero, but alas it was also rather confusing.
Or, perhaps, is the Zero's labelled SDA (and SCL) actually an independent pin, not ganged to any of the D or A sockets on the board headers?
I realise this is probably a Classic Stupid Question -- but I did google fairly diligently w/o finding an answer at my comprehension level.