/**
 * Registers a document as a style injection target.
 *
 * Existing registered styles are replayed into the document immediately.
 * Documents are reference-counted so multiple providers can safely register the
 * same document without one cleanup removing it while another registration is
 * still active.
 *
 * @param targetDocument Document to receive registered styles.
 * @return Cleanup function that unregisters this document registration.
 */
export declare function registerDocument(targetDocument: Document): () => void;
/**
 * Registers a style and injects it into all registered documents.
 *
 * The hash is used as the deduplication key, so calling this repeatedly with
 * the same hash will not add duplicate style tags to a document.
 * Registered styles are retained for the lifetime of the page so they can be
 * replayed into documents that are registered later.
 *
 * @param hash Stable hash for the transformed CSS.
 * @param css  CSS text to inject.
 */
export declare function registerStyle(hash: string, css: string): void;
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