```ts
/** Text with the case of every letter turned over. */
export function swapCase(text: string): string {
  return text.split('').map(char => {
    if (char.match(/[a-zA-Z]/)) {
      return char === char.toUpperCase() ? char.toLowerCase() : char.toUpperCase();
    } else {
      return char;
    }
  }).join('');
}
```