3.3.3. Customizing class creation
3.1/3.2 docs say
"If the metaclass keyword argument is based with the bases, it is used."
(new version for 3.x) I presume 'based' was meant to be 'passed'.

However, with that correction, would it really be correct?
I presume the metaclass compatibility issue discussed in #1294232 for
2.x is still relevant for 3.x.

The next line
"Otherwise, if there is at least one base class, its metaclass is used."
(same as for 2.x docs) does not say which 'its' is used if there is more
than one. See paragraph above and #1294232.

I do not know the actual rule well enough to improve the neglected
suggestion in the referenced issue.