/**
 * Checks if a string starts with a given prefix, ignoring case.
 * @param {string} str - The string to check.
 * @param {string} prefix - The prefix to check for.
 * @returns {boolean} - True if the string starts with the prefix, ignoring case.
 * @example startsWithIgnoreCase('Hello, world!', 'hello') // true
 * @example startsWithIgnoreCase('Hello, world!', 'world') // false
 */
export declare function startsWithIgnoreCase(str?: string, prefix?: string): boolean;