Examine source code of GTM variables move

{
  "name": "GTM variables move",
  "version": "0.0.0.6",
  "description": "Moves Userdefined variables before builtinvariables in GTM variables view",
  "manifest_version": 2,
  "author": "Bendik Knapstad",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "https://tagmanager.google.com/*",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://tagmanager.google.com/*"
      ],
      "js": [
        "background.js"
      ],
      "run_at": "document_end"
    }
  ],
  "icons": {
    "16": "icon-16.png",
    "48": "icon-48.png",
    "128": "icon-128.png"
  }
}