@DavidCarlisle or @egreg -- In question
tex.stackexchange.com/q/520375 , the OP is using
\[...\]
with
\tag
and a label. (This is with
amsmath
via
amsart
.) I think that a label won't work here, but I'm not sure; what I
am pretty sure about is that, if it doesn't work, it isn't documented. So my question is, shouldn't it be documented?