/**
 * A variant of `lit/directives/if-defined` which stops rendering if the given value is
 * not a number in addition to  `null`/`undefined`.
 *
 * For AttributeParts, sets the attribute if the value is defined and a number, and removes
 * the attribute if the value is undefined not a number.
 *
 * For other part types, this directive is a no-op.
 *
 * @param value
 */
export declare function ifNumber(value: number | undefined): number | typeof import("lit-html").nothing;