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  "title" : "Internal symbols"
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# Internal symbols

Restricted-use symbols that the framework requires for macro expansion and
other internal tasks.

## Discussion> Important: Don’t use these restricted symbols directly. The framework depends
> on the symbols for macro expansion and other nonpublic tasks.

## Topics

### Storage

[`protocol BackingData`](/documentation/SwiftData/BackingData)

An interface for providing in-memory storage for a persistent model.


---

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