Update models documentation

**Problem**
When working with lib, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Locate the models documentation and the error-handling code under lib, since the issue names no specific file or test. Read the surrounding guidance and existing error paths first; done means a concrete documentation update with detailed error messages and a defined validation step.

Written by the indexing model from the issue text.