/**
 * Validates if a string is a valid email address according to RFC 5322 standards.
 *
 * This function performs comprehensive validation including:
 * - Basic email structure (local part + @ + domain)
 * - Valid characters in local part and domain
 * - Domain must contain at least one dot
 * - No consecutive dots
 * - No trailing dots or hyphens
 * - Length limits (local part ≤ 64 chars, domain ≤ 255 chars)
 * - Non-ASCII character rejection
 *
 * @param text - The string to validate as an email address
 * @returns boolean indicating if the string is a valid email address
 *
 * @example
 * ```typescript
 * isEmail('user@example.com')     // true
 * isEmail('user.name@example.com') // true
 * isEmail('user+tag@example.com') // true
 * isEmail('plainaddress')         // false
 * isEmail('@example.com')         // false
 * isEmail('user@')               // false
 * ```
 */
export declare function isEmail(text: string): boolean;