Examine source code of ytHideWatched

{
  "manifest_version": 2,
  "name": "ytHideWatched",
  "version": "0.11",
  "author": "Mighty Elk",
  "description": "Hides already watched videos on Youtube channels and feeds.",
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/c/*",
        "*://www.youtube.com/feed/*",
        "*://www.youtube.com/user/*"
      ],
      "js": [
        "jquery-3.4.1.min.js",
        "main.js"
      ]
    }
  ]
}