Refactor lib for better readability

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

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

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

No files, tests, or entry points are named. Start by locating the validation and error-handling code in lib and reviewing how current errors are generated. Done means the relevant error messages are more descriptive and the refactoring improves readability without changing validation behavior.

Written by the indexing model from the issue text.