Yes. `getHeaders` should return something like:

```php
[
  header name -> header value,
  header name -> [header value1, header value2],
]
```

It's not only `Cache-Control` that can have multiple values.  For example:

```
WWW-Authenticate: Negotiate 
WWW-Authenticate: Basic realm="EXAMPLE.COM" 
```

So setting headers should support arrays as well.