Type Alias ScreenItemDefinition<Id, Input, Data, State, E, R, Actions, Host, Top>

ScreenItemDefinition: ScreenShape<
    Id,
    "item",
    Input,
    Data,
    State,
    E,
    R,
    Actions,
    Host,
    Top,
> & {
    host: ScreenCodec<Host, unknown>
    | undefined;
    is: (
        value: unknown,
    ) => value is ScreenInstance<
        ScreenShape<Id, "item", Input, Data, State, E, R, Actions, Host, Top>,
    >;
}

An item definition: what defineScreenItem returns and a host's item list names.

Readonlyhost: ScreenCodec<Host, unknown> | undefined
The schema of the state of the screen the item is shown on, which the item's state reads (host): the item's actions see the host's facts — the thread a message belongs to — without a copy of them in each entry. Absent when the item reads nothing of its host. The host screen's state must fit it: a misfit is a type error in the platform's screenSet.
Readonlyis: (
value: unknown,
) => value is ScreenInstance<
ScreenShape<Id, "item", Input, Data, State, E, R, Actions, Host, Top>,
>
Whether value is this item's handle: the narrowing of a union of item handles — the same guard a screen definition carries, written XxxItem.is(handle).