$ irb
irb(main):001:0> Hash.instance_methods.include? "map"
=> true

So one would expect "map" to appear under "Instance methods" in ri.
Of course it comes from a mixin.  That's not the issue here.  The
existence of this thread is a data point.

Thus ensues the eternal struggle between those who are accustomed to
the idiosyncrasies and those who are driven insane by them.