Support adding/removing from element metadata array

When extending existing element it is sometimes desirable to just add or remove an item from an array.

Consider the following <my-component> component wrapping an <input> element and dynamically binding all attributes from the component:

<input type="text" :attrs="attrs">

Suitable element metadata would be:

{
  "my-component": {
    "inherit": "input"
  }
}

Since <input> requires type to be set ("requiredAttributes": ["type"]) usage of <my-component> would yield errors despite the underlying <input> element having the type attribute.

Setting requiredAttributes to an empty array would reset the attribute but possibly remove other unwanted attributes from the array. It would be useful to have a method of removing elements from the array without resetting it.

Suggested solution

Support setting requiredAttributes to ["-type"] to remove type when merging the array without removing other entries. Similarly a + could be used to add entries. This would have issues with non-string types and if the item has an actual leading + or -, i.e. consider an attribute such as tabindex="-1".

Perhaps the array could be specified with an object structure similar to:

"requiredAttributes": {
  "add": ["foo"],
  "remove": ["bar"]
}