/**
 * Validates that a URL uses a safe protocol (http: or https:) and
 * returns it, or returns undefined if the URL is invalid/unsafe.
 */
export declare function sanitizeUrl(url: string | undefined | null): string | undefined;
/**
 * Sanitizes a URL for use in CSS url() context by validating the protocol
 * and percent-encoding characters that could break out of url('...').
 */
export declare function sanitizeCssUrl(url: string | undefined | null): string | undefined;