How to keep primitive custom attribute

[andy259]

Hi,
I hvae a custom attribute _BATCHID in the primitives. when I use -tc -noq to do it, the _BATCHID is gone.
How can I keeep the attribute _BATCHID ?
Thanks.

"primitives": [
    {
      "mode": 4,
      "attributes": {
        "POSITION": 376,
        "NORMAL": 377,
        "TEXCOORD_0": 378,
        "_BATCHID": 379
      },
      "material": 0
    }
  ]

[zeux]

Right now gltfpack doesn't preserve unknown attributes. Is _BATCHID related to 3D tiles or some extension like this? If this is common enough it might make sense to support out of the box, but I'd need a test model for this.