/**
 * Bollinger Band Width (BBW).
 * Returns the normalized width of the Bollinger Bands as percentage: `100*(upper-lower)/middle`.
 * NaNs propagate and positions with `middle === 0` leave the output unchanged (NaN or 0).
 * @param source Input series
 * @param period Window length
 * @param mult Standard-deviation multiplier used for BB
 * @returns Float64Array of BB width percentages
 */
export declare function bbw(source: ArrayLike<number>, period: number, mult: number): Float64Array;