top level reference is not supported

[royling]

Given the below schema:

{
  "definitions": {
    "input": { "type": "string" }
  },
  "$ref": "#/definitions/input"
}

The form can not be generated.

[daniele-pecora]

This may require to compile the json schema before handig it over to sf-form.

The solutio to this is provided in #319