Examine source code of Apple Music Extended

{
  "manifest_version": 2,
  "name": "Apple Music Extended",
  "version": "1.2",
  "description": "Hotkey and notification for apple music.",
  "icons": {
    "64": "amext.png"
  },
  "permissions": [
    "notifications",
    "tabs"
  ],
  "commands": {
    "pause": {
      "suggested_key": {
        "default": "Shift+Alt+J"
      },
      "description": "Play/Pause"
    },
    "next-song": {
      "suggested_key": {
        "default": "Shift+Alt+N"
      },
      "description": "Play the next song"
    },
    "previous-song": {
      "suggested_key": {
        "default": "Shift+Alt+P"
      },
      "description": "Play the previous song"
    }
  },
  "background": {
    "scripts": [
      "amext_bg.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://music.apple.com/*",
        "*://beta.music.apple.com/*"
      ],
      "js": [
        "amext_content.js"
      ]
    }
  ]
}