Examine source code of Slack App-in-Tab

{
  "name": "Slack App-in-Tab",
  "description": "Open the slack app in your browser to switch between multiple workspaces in a single tab",
  "version": "1.0",
  "manifest_version": 2,
  "icons": {
    "48": "slack-app-in-tab-logo-48x48.png",
    "128": "slack-app-in-tab-logo-128x128.png"
  },
  "content_scripts": [
    {
      "js": [
        "contentScript.js"
      ],
      "matches": [
        "https://*.slack.com/*"
      ],
      "run_at": "document_start"
    }
  ],
  "permissions": [
    "activeTab",
    "tabs",
    "https://*.slack.com/*"
  ]
}