Time format when showing all data in tooltip

[the21st]

I want to set up a chart where the tooltip shows all fields of a datum. So I'm using

  "mark": {
    "type": "bar",
    "tooltip": {"content": "data"}
  },

However, the time field in the tooltip shows what seems to be the timestamp in the epoch (seconds) format, which is just not very readable for humans:

This is the full spec (it was generated by altair)

Is there anything I can do to format the time to a human-readable format, while keeping the "tooltip": {"content": "data"} option?

[kanitw]

I think this requires modification to the library, so I'm filing this issue #7652.