/**
 * Utility function that allows to construct class names from block and element names
 * @example bem('ce-popover)() -> 'ce-popover'
 * @example bem('ce-popover)('container') -> 'ce-popover__container'
 * @example bem('ce-popover)('container', 'hidden') -> 'ce-popover__container--hidden'
 * @example bem('ce-popover)(null, 'hidden') -> 'ce-popover--hidden'
 * @param blockName - string with block name
 */
export declare function bem(blockName: string): (elementName?: string | null, modifier?: string) => string;