Examine source code of Hide Checkmarks

{
  "manifest_version": 2,
  "name": "HideCheckmarks",
  "version": "1.1",
  "description": "removes verification checkmark from youtube",
  "icons": {
    "48": "icons/check.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "checkmark.js"
      ]
    }
  ]
}