AppFlowy/frontend/app_flowy/packages/flowy_editor/assets/document.json

{
  "document": {
    "type": "root",
    "children": [
      {
        "type": "text",
        "attributes": {
          "text-type": "heading1"
        }
      },
      {
        "type": "text", 
        "attributes": {
          "tag": "*"
        },
        "children": [
          {
            "type": "text",
            "attributes": {
              "text-type": "check-box",
              "check": true
            }
          },
          {
            "type": "text",
            "attributes": {
              "tag": "**"
            }
          }
        ]
      },
      {
        "type": "image",
        "attributes": {
          "url": "x.png"
        }
      },
      {
        "type": "video",
        "attributes": {
          "url": "x.mp4"
        }
      }
    ]
  }
}