$recursiveRef: only supports hash fragment reference

AJV: 8.6.2
Draft: 2019-09

Hi, I've run into into a issue with `$recursiveAnchor` and `$recursiveRef` where I'm unable to target non-root schemas using `$recursiveRef`. For simplicity, below is the TypeScript data structure I'm trying to represent in JSON schema.

```typescript
interface Element {
elementId: string
elements: Element[]
}

interface Node {
nodeId: string
nodes: Node[]
element: Element
}
```
The following is the JSON schema I'm using to represent the above type. I believe JSON schema interprets the `#` pointer in the following to refer to the root schema in nested schemas, causing the inner `Element` array to be interpreted as an array of type `Node`. This is expected behaviour.
```
{
"additionalProperties": false,
"$id": "Node", // <------------+
"$recursiveAnchor": true, // |
"type": "object", // |
"properties": { // |
"nodeId": { // |
"type": "string" // |
}, // |
"nodes": { // |
"type": "array", // | { $recursiveRef: '#' } targets root schema "Node"
"items": { // |
"$recursiveRef": "#" // -------------+
} // |
}, // |
"element": { // |
"additionalProperties": false, // |
"$id": "Element", // |
"$recursiveAnchor": true, // |
"type": "object", // |
"properties": { // |
"elementId": { // |
"type": "string" // |
}, // |
"elements": { // |
"type": "array", // |
"items": { // |
"$recursiveRef": "#" // -------------+
}
}
}
}
}
}
```
To address this, I've tried passing an explicit JSON pointer to try and target the appropriate sub schema.
```
{
"additionalProperties": false,
"$id": "Node", // <------------+
"$recursiveAnchor": true, // |
"type": "object", // | Array of Node
"properties": { // |
"nodeId": { // |
"type": "string" // |
}, // |
"nodes": { // |
"type": "array", // |
"items": { // |
"$recursiveRef": "Node#" // -------------+
}
},
"element": {
"additionalProperties": false,
"$id": "Element", // <------------+
"$recursiveAnchor": true, // |
"type": "object", // | Array of Element
"properties": { // |
"elementId": { // |
"type": "string" // |
}, // |
"elements": { // |
"type": "array", // |
"items": { // |
"$recursiveRef": "Element#" // -------------+
}
}
}
}
}
}
```
However, AJV is reporting the following for the second schema.
```
Error: "$recursiveRef" only supports hash fragment reference
```
Not sure if this is against specification, or a possible constraint with some of the architectural changes in AJV to support these newer drafts. I've come across https://github.com/ajv-validator/ajv/issues/1198 which suggests dynamic ref scoping (which I'm guessing relates to this) So not sure if this is working as intended or is a bug. However, I've tested the second schema in [JSON.NET Schema](https://www.jsonschemavalidator.net/) which seems to support referencing of this kind. So not sure.

**What do you think is the correct solution to problem?**

Allow `$recursiveRef` to support `$id` referencing.