... is this different from the previous proposal...

Yes. The "use base" technique makes one class inherit from the other, whereas this technique makes the two namespaces equivalent.

A key difference is that inheritance only works for method calls, whereas namespace aliasing works for both methods and function calls.

Where is it possible to find the doc of the 'use base ...;' construct?

The base module is included with Perl, so you should be able to run perldoc base for documentation.