Examine source code of Better Ruler

{
  "name": "Better Ruler",
  "short_name": "Ruler",
  "version": "1.2.6",
  "manifest_version": 2,
  "default_locale": "zh_CN",
  "description": "__MSG_pluginDesc__",
  "author": "paul",
  "icons": {
    "128": "icon.png"
  },
  "browser_action": {
    "default_title": "Better Ruler",
    "default_icon": "icon.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "web_accessible_resources": [
    "css.css"
  ]
}