[Question] Stance about key duplication

I have a question about the stance of the library against key dupclication.

Currently, there is no key duplication check on construct, and the operators work even if there is a key duplication.
There is a metion in the README about fixing `KeyDoesNotExist` and `RemoveAccessTo`, which I guess you want to get rid of key duplication. But then there are operators like `append` that could bring in key duplication.
So which stance does the library have(or will have) against key duplication?

1. Prevent key duplication by adding key check constraints on construct functions/instances and make sure operations don't bring in key duplication.
2. Adding key check constraints are costly, so don't. Make the operation works even if there ia an accidentaly brought in key duplication.

Start with the README references to KeyDoesNotExist and RemoveAccessTo, then inspect the construct functions or instances and the append operator mentioned in the issue. This issue needs a maintainer decision on the library's key-duplication policy before an implementation can be scoped.

Written by the indexing model from the issue text.