[Bold]a part in bold [/BOLd] not in bold [B]bold, [/B]not bold
[UNDERliNe]underlined piece

§la part in bold §r not in bold §lbold, §rnot bold§nunderlined piece

[
  {
    "text": "",
    "extra": [
      {
        "text": "",
        "extra": [
          {
            "text": "a part in bold ",
            "bold": true
          },
          " not in bold ",
          {
            "text": "bold, ",
            "bold": true
          },
          "not bold"
        ]
      },
      {
        "text": "underlined piece",
        "underlined": true
      }
    ]
  }
]