/**
 * True for a URL that is safe to persist as an uploaded-file ref and to
 * render as an `href`: `http:`/`https:` or relative (no scheme). Browsers
 * drop leading control characters and spaces, and tabs/newlines anywhere,
 * before parsing the scheme, so `" java\tscript:"` is normalised the same way.
 */
export declare function isSafeUrl(url: string): boolean;