Examine source code of YouTube Autofocus

{
  "manifest_version": 2,
  "name": "YouTube Autofocus",
  "version": "1.0",
  "description": "Automatically focuses on search bar when YouTube is opened",
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/"
      ],
      "js": [
        "autofocus.js"
      ]
    }
  ],
  "icons": {
    "16": "search16.png",
    "128": "search128.png"
  }
}