> ## Documentation Index
> Fetch the complete documentation index at: https://docs.devin.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# messageSubIndex

```typescript
messageSubIndex(payload: unknown): undefined | number
```

The ordering sub-index of a chunk within its message.

## Parameters

**payload** `unknown` *required*

## Returns

`undefined | number`


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