> Here I was talking about what is auto-completed, when this library is connected to another project via Composer

I know. But your problem is caused by PhpStorm, not by Composer. Most libraries have unit-test classes in a sub-namespace - excluding it from analysis is something I do on most projects, it's not really a "problem".

The demo belongs in a sub-namespace, e.g. `mindplay\annotations\demo`, if you want to comply with PSR-0 - `demo\anything` would be a clear violation, since your vendor-name is not `demo`.