Referencing arrays in function bindings in HTTP triggered functions

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#### What language does your question apply to? (e.g. C#, JavaScript, Java, All)
Javascript

#### Question
I'm trying to figure out how to reference array properties in binding expressions from the request body of an Http triggered function. I can't find any documentation on it, and everything I've tried doesnt work:

- `arr.0.property`
- Fails with the error message: `Error while accessing 'arr': property doesn't exist.`
- `arr.*.property`
- Fails with an invalid binding expression
- `arr[0].property`
- Fails with an invalid binding expression
- `arr.property`
- Fails with the error message: `Error while accessing 'arr': property doesn't exist.`

Here's an example request body:
```
{
"arr": [{
"property": "val"
}]
}
```

Here is my `function.json`:
```
{
"bindings": [
{
"authLevel": "anonymous",
"type": "httpTrigger",
"direction": "in",
"name": "req",
"route" :"{path}/{id?}",
"methods": [
"get",
"post"
]
},
{
"type": "http",
"direction": "out",
"name": "res"
},
{
"name": "blobOutput",
"type": "blob",
"path": "container/{arr.0.property}"
"direction": "out"
}
],
"scriptFile": "../dist/function/index.js"
}
```

Any guidance would be great. Thanks

Start with the binding-expression documentation and the shown function.json, then compare the attempted array expressions with the HTTP request body example. Done means documenting the supported syntax for array properties, or clearly stating the limitation and any supported alternative.

Written by the indexing model from the issue text.