# invariants
- `State<T>` cannot be a parameter to a struct implementing `Component`
- this might only be true of the root component
- `use_state` (and other hooks) can only be called in `render`
- if you take children in your custom component you must call `render` on them when being rendered
- frozen / rendred structs should only take in `AnyElement` not `AnyComponent`
- all components should take in a `on_key` parameter
- custom components must implement `Default`
# todo
- add a conditional component
- make `KeyHandler` have a return type, specifically something like a `Continue`,
for `KeyEvent` propagation.