export declare function toString(v: any): string;
/**
 * Mask a portion of a string with a repeated character, Laravel-style
 * (stacksjs/stacks#314).
 *
 * Useful for redacting PII in logs (credit card middle, phone digits,
 * email local part) without losing the format. The mask character is
 * repeated for `length` characters starting at `index`; `length` defaults
 * to "all remaining characters from index to end of string."
 *
 * `index` is the character offset, not a byte offset. Negative `index`
 * counts from the end of the string (`-4` = "start four characters from
 * the end"). An out-of-range `index` returns the original string.
 *
 * @example
 * ```ts
 * mask('1234567890123456', '*', 4, 8)   // → '1234********3456'
 * mask('1234567890123456', '*', 4)      // → '1234************'
 * mask('1234567890123456', '*', -4, 4)  // → '123456789012****'
 * mask('hello@example.com', '*', 1, 4)  // → 'h****@example.com'
 * ```
 */
export declare function mask(value: string, character: string, index: number, length?: number): string;