function isValidEmail(email) {
  // This regex validates common email formats (e.g., user@domain.com, user.name@sub.domain.co).
  // It does not cover all edge cases defined by RFCs but is sufficient for most web applications.
  const emailRegex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
  return emailRegex.test(email);
}

// Example Usage:
// const email1 = "test.user@example.com";
// const email2 = "invalid-email";
// console.log(`'${email1}' is valid: ${isValidEmail(email1)}`);
// console.log(`'${email2}' is valid: ${isValidEmail(email2)}`);