/**
 * @packageDocumentation Case-insensitive key-value container for audio metadata properties.
 */
/**
 * A case-insensitive key-value container for audio metadata properties.
 * Keys are normalised to uppercase (e.g. `"TITLE"`, `"ARTIST"`).
 *
 * Mirrors the TagLib `PropertyMap` API. Each key maps to an ordered list of
 * string values, allowing multi-valued tags such as multiple artists.
 */
export declare class PropertyMap {
    /** Internal storage — keys are always stored in uppercase. */
    private _map;
    /** Keys from the original tag that this map does not know how to represent. */
    private _unsupported;
    /** Converts `key` to its canonical uppercase form used for storage. */
    private static normalizeKey;
    /** The number of distinct keys in the map. */
    get size(): number;
    /** Insert (append) values for a key. */
    insert(key: string, values: string[]): void;
    /** Replace all values for a key. */
    replace(key: string, values: string[]): void;
    /** Check whether a key exists (case-insensitive). */
    contains(key: string): boolean;
    /** Get values for a key, or undefined if not present. */
    get(key: string): string[] | undefined;
    /** Remove a key. Returns true if the key existed. */
    erase(key: string): boolean;
    /** Iterate over all entries. */
    entries(): IterableIterator<[string, string[]]>;
    /** Iterate over all keys. */
    keys(): IterableIterator<string>;
    /** Remove all entries. */
    clear(): void;
    /** Merge another PropertyMap into this one (concatenating values). */
    merge(other: PropertyMap): void;
    /** Remove entries whose value arrays are empty. */
    removeEmpty(): void;
    /**
     * Returns a copy of the list of keys that could not be mapped to a
     * standard property name.
     */
    unsupportedData(): string[];
    /**
     * Records `key` as an unsupported tag field that this map cannot represent.
     *
     * @param key - The raw tag key to mark as unsupported.
     */
    addUnsupportedData(key: string): void;
    /** Returns a human-readable representation of the map and unsupported keys. */
    toString(): string;
}
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