/**
 * Copies text to the browser's clipboard.
 * Uses the modern `navigator.clipboard` API, with a fallback to `document.execCommand` when unavailable.
 * @param {string} text Text to copy to the clipboard
 * @returns {Promise<void>} Promise that resolves on successful copy or rejects on error
 * @throws {Error} Throws an error if neither `navigator.clipboard` nor `document` is available
 * @example
 * ```typescript
 * // Copy simple text
 * copyText('Hello, World!')
 *   .then(() => console.log('Text copied'))
 *   .catch(error => console.error('Copy error:', error));
 *
 * // Using with async/await
 * try {
 *   await copyText('Text to copy');
 *   console.log('Successfully copied');
 * } catch (error) {
 *   console.error('Failed to copy:', error);
 * }
 * ```
 */
export declare function copyText(text: string): Promise<void>;