# Deep into the framework

- [Register Additional Authenticators](/v3.0/deep-into-the-framework/register-authenticators.md)
- [Debugging](/v3.0/deep-into-the-framework/debugging.md)
- [User Verification](/v3.0/deep-into-the-framework/user-verification.md)
- [Attestation and Metadata Statement](/v3.0/deep-into-the-framework/attestation-and-metadata-statement.md)
- [Authenticator Selection Criteria](/v3.0/deep-into-the-framework/authenticator-selection-criteria.md)
- [Authentication without username](/v3.0/deep-into-the-framework/authentication-without-username.md)
- [Extensions](/v3.0/deep-into-the-framework/extensions.md)
- [Token Binding](/v3.0/deep-into-the-framework/token-binding.md)
- [Authenticator Counter](/v3.0/deep-into-the-framework/authenticator-counter.md)
- [Dealing with “localhost”](/v3.0/deep-into-the-framework/dealing-with-localhost.md): aka non-https relying parties