Restrict property definitions to specific tags

I've looked through the information here and several other sites and JSON documents, and the one thing I cannot find an answer to, is how to define a property for only certain tags. For example, NativeScript supports a placeholder-color property on the TextField tag, but VSCode does not recognize it. I've added it as a property to a CSS custom data file as described, but that makes the property available to ALL tags -- not just the TextField tag. If this is indeed new functionality, then I suggest that the property object contain a tags property which would be an array of strings.

{
  "version": 1.1,
  "properties": [
    {
      "name": "placeholder-color",
      "description": "Color of the placeholder text.",
      "tags": ["TextField", "Button"]
    }
  ]
}

On the other hand, if this is already supported in some way, could you please make it more clear in your documents?

Thanks!
Eric

Start with the custom data format documentation and the property-definition behavior described in this issue. Verify whether tag-scoped properties are already supported; done means documenting the existing syntax or agreeing on and implementing the proposed tags restriction.