/** The tags the library ships its own catalog for — their library namespaces are reserved. */
export declare function isBuiltInLocale(tag: string): boolean;
/** `pt-br` → `pt-BR`. Throws `RangeError` on a string that is not a well-formed BCP-47 tag. */
export declare function canonicalLocaleTag(tag: string): string;
/** @internal Called by `registerLocale` only. */
export declare function markLocaleRegistered(tag: string): void;
export declare function getRegisteredLocales(): readonly string[];
/**
 * The registered tag that serves `tag`, by BCP-47 lookup (RFC 4647 §3.4): the exact tag first,
 * then the tag with its last subtag removed, and so on — `de-AT` is served by `de`, `ja-JP` by
 * `ja`. `undefined` when nothing registered matches.
 */
export declare function resolveRegisteredLocale(tag: string | null | undefined): string | undefined;
/** `<html lang>` when it names a registered locale. Read at CALL time — `lang` is often set late. */
export declare function resolvePageLocale(): string | undefined;
/**
 * The locale nothing chose (decision A2): the page's `<html lang>` if it is registered, else
 * `en`. NEVER `navigator.language` — a server cannot see it, so the first client render would
 * disagree with the server's HTML.
 */
export declare function resolveDefaultLocale(): string;
/** One development warning per unknown tag, then silence. */
export declare function warnUnknownLocale(tag: string, fallback: string): void;
/** Test seam: the once-per-tag warning is module state. */
export declare function resetUnknownLocaleWarningsForTests(): void;