{
  "preamble": "preamble that is only for comments\n",
  "parts": {
    "text": {
      "headers": {
        "Content-Disposition": {
          "name": "text",
          "subtype": "inline"
        }
      },
      "content": "text default"
    },
    "file1": {
      "headers": {
        "Content-Disposition": {
          "name": "file1",
          "filename": "a.txt",
          "subtype": "form-data"
        },
        "Content-Type": "text/plain"
      },
      "content": "Content of a.txt.\n"
    }
  }
}