Let's say an XML Schema schema A uses types from another schema B.
Then, if I understand things correctly, A needs to import schema B
(maybe "importing its namespace" is more correctly put). It is also
allowed for both A and B to import the XML Schema namespace, but at
least when I use the xmllint validator, it isn't necessary.
My question is, is it ever necessary to import the XML Schema
namespace? If not necessary, when might it be useful?