Examine source code of VoiceHack

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "VoiceHack",
  "short_name": "VoiceHack VK",
  "permissions": [
    "storage",
    "*://*.vk.com/*",
    "*://*.vk.me/*",
    "*://*.userapi.com/*"
  ],
  "description": "Распознавание голосовых сообщений.",
  "version": "2.3",
  "icons": {
    "16": "icons/16.png",
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/16.png",
      "48": "icons/48.png",
      "128": "icons/128.png"
    },
    "default_title": "VoiceHack",
    "default_popup": "popup/popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://vk.com/*"
      ],
      "css": [
        "style.css"
      ],
      "js": [
        "vk.js"
      ],
      "run_at": "document_end"
    }
  ],
  "background": {
    "scripts": [
      "jquery.js",
      "background.js"
    ],
    "persistent": true
  },
  "manifest_version": 2
}