encoding.order sort the path not the stack for Q-Q area chart

[yhoonkim]

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      {"a": 1, "b": 2, "c": "c1"},
      {"a": 2, "b": 3, "c": "c1"},
      {"a": 3, "b": 1, "c": "c1"},
      {"a": 1, "b": 2, "c": "c2"},
      {"a": 3, "b": 1, "c": "c2"},
      {"a": 2, "b": 2, "c": "c2"}
    ]
  },
  "mark": "area",
  "encoding": {
    "x": {"field": "a", "type": "quantitative"},
    "y": {"field": "b", "type": "quantitative"},
    "color": {"field": "c"},
    "order": {"field": "c"}
  }
}

The main reason is that Area chart is not stacking with x:Q and y:Q by default so that "order" channel apply the sort on the path rather than the stacking order.

I suggest to stack by default for bar (=stacking the color even without stack def) like bar.