states that value member named “size” is “the size of this mutable hash map” .
Isn’t that a misleading (or at least unhelpful) description? There are several “sizes” which one might want to know, and this documentation does not indicate which one it is. Size could mean the amount of allocated space, the size of the underlying sparse array, the number of key->value pairs stored in the hash map, or potentially several more.
In my option, the documentation would be more helpful if it really indicated more than what is obvious given the name of the value member.
BTW, which one is it?