Update api documentation

**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 file or test is named. Start by locating the validation error-handling entry points and the API documentation, then determine the intended message details. Done means validation failures provide more descriptive errors and the API documentation reflects the change.

Written by the indexing model from the issue text.