Advanced Usage

Five pages cover everything beyond the basics. Each is scoped to one mental model — pick the one that matches your problem.

Page	Use it when
Cross-Field Validation	One field's rule depends on another. Covers Ref (declarative) and the __monk_validate__ hook (programmatic).
Context-Aware Validation	A rule depends on data outside the model (current user, tenant config, clock, feature flags). Covers Ctx and the __monk_validate__(self, context) overload.
Customization	You want custom error messages, custom error codes, or you are building your own constraint.
Execution Models	You hit the edges of validate_dict (partial, sanitization), need streaming validation, or want recursive / nested schemas.
Settings and Type Metadata	You are integrating with a framework that wraps values, uses sentinels, or expresses optionality through a custom generic.

If your question is "what does built-in constraint X do?", that lives in the Constraints catalog instead.