/**
 * A collection that takes both an array prop and declarative children renders the prop when
 * both are set (`src/components/_agents/slot-patterns.md`, "Collections with two APIs").
 */
/** Whether `items` is a non-empty array, i.e. the prop is the source that renders. */
export declare const usesItemsProp: (items: readonly unknown[] | undefined) => boolean;
/**
 * Warns once per host when `items` is set and the host also has `childTag` children,
 * which the prop overrides.
 */
export declare function warnIfBothSources(host: HTMLElement, items: readonly unknown[] | undefined, propName: string, childTag: string): void;