Update validation documentation

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

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

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

The issue names no files, tests, or entry points. Start by locating the validation helpers and their current documentation, then identify the existing error-message behavior; done means the documentation clearly specifies the intended validation errors and examples for debugging.

Written by the indexing model from the issue text.