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# kQLPreviewContentIDScheme

The content ID URL scheme.

```
let kQLPreviewContentIDScheme: CFString!
```

## Discussion

The `cid` URL scheme permits the HTML of a mail message to refer to the images or other data included in the message. For more information, read [RFC 2111](https://www.rfc-archive.org/getrfc.php?rfc=2111).

---

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