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Don't bother. US ISO doesn't actually exist; it's only a crutch we use to refer to basic ISO support (the bare minimum 4 keys needed for physical compatibility) for sets that don't want to provide an actual, full ISO kit (like ISO-UK).
While it's true that it won't get used as much, I wouldn't go as far as saying that "US ISO" doesn't exist. US ISO
does exist, even if it's seldom seen. The official definition is that, indeed, when trading the horizontal ("ANSI") Enter key with a vertical ("ISO") one, the R2 1.5U
\| key is replaced by the one in the R3 1.0U space left behind. It is, surprisingly enough, the R4 key between left Shift and Z that gets to be the "repeated" key, and for which alternatives exist (some terminal keyboards put
<> there; some others forego it and put a long left Shift key, making for an ANSISO hybrid keyboard).
That said, if UK ISO is fully supported, everything is fine. Getting UK
+US ISO fully supported, with the addition of one single key (for which molds exist, yadda yadda yadda), would be a welcome bonus.
The "barebones" ISO support we've talked about in the other thread (1.25U left Shift, ISO Enter, R3
\| and R4
\|) is what gives complete physical
("no naked switches") support for ISO and that preserves maximum flexibility at a minimum number of additional keys (four) for ISO support,
on a kit built from the ground up for an ANSI keyboard with the US English layout on top, as is the case with pretty much all of the extant ones.