Registers "default return values" no longer mentioned

[Smileynator]

I remember in the past the go-to advice was that any register not explicitly having a function or any "bits" not used in a register, by default are "tied high" and thus return 1.
In the pandocs i cannot find this mentioned on some random registers with this behavior, nor in general on the I/O ranges chapter.

If the information is still in there, it might be too hard to find as is.

Another question is if that data is accurate, pins might be floating, i am unsure of specific evidence on what those pins should do. If floating is the answer, that should probably be mentioned instead, and then it is up to the emu-dev to resolve.

[ISSOtm]

AFAIK they are indeed floating, but the pull-ups on internal busses always make them return 0. cc @LIJI32 and @CasualPokePlayer for confirmation on that point.

Where would it be appropriate to write that down, too?

[LIJI32]

Unused register bits (as well as unused register addresses) typically return 1s, not 0s.