Forms and Validation in Reactor

Reactor forms use a controlled-input pattern — every input has an explicit (value, setter) pair driven by UseState. There is no two-way binding. Validation is layered on top via UseValidationContext and declarative .Validate() modifiers.

Controlled prop note: factory call sites keep the plain (value, setter) shape, but the underlying element records use Optional<T>. Read element props with .Value / .GetValueOrDefault(...); use Optional<T>.Unset only when the WinUI control should own the value. See migration/050-optional-t.md.

Quick reference