/**
 * Pads the start of a string with another string until the target length is reached
 *
 * @param {string} string_ - The original string to pad
 * @param {number} targetLength - The target length after padding
 * @param {string} padString - The string to use for padding
 * @returns {string} The padded string
 * @example
 * ```typescript
 * padStart("123", 5, "0");     // Returns: "00123"
 * padStart("abc", 8, "def");   // Returns: "defdeabc"
 * ```
 */
export declare const padStart: (string_: string, targetLength: number, padString: string) => string;