Examine source code of PageMark

{
  "description": "Mark a page | Keep your place | Make some notes",
  "manifest_version": 2,
  "name": "PageMark",
  "version": "1.4.4",
  "homepage_url": "http://pixelgiant.co",
  "icons": {
    "16": "icons/mark-16.png",
    "32": "icons/mark-32.png",
    "48": "icons/mark-48.png",
    "96": "icons/mark-96.png"
  },
  "permissions": [
    "contextMenus",
    "tabs",
    "activeTab",
    "downloads",
    "menus"
  ],
  "background": {
    "scripts": [
      "background-script.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "exclude_matches": [
        "*://mail.google.com/*",
        "*://*.twitter.com/*",
        "*://*.facebook.com/*",
        "*://mail.yahoo.com/*"
      ],
      "js": [
        "content-script.js"
      ],
      "css": [
        "css/content-style.css"
      ]
    }
  ],
  "browser_action": {
    "browser_style": true,
    "default_title": "PageMark",
    "default_icon": "icons/mark-48.png",
    "theme_icons": [
      {
        "light": "icons/mark-96.png",
        "dark": "icons/mark-96.png",
        "size": 96
      },
      {
        "light": "icons/mark-48.png",
        "dark": "icons/mark-48.png",
        "size": 48
      },
      {
        "light": "icons/mark-32.png",
        "dark": "icons/mark-32.png",
        "size": 32
      },
      {
        "light": "icons/mark-16.png",
        "dark": "icons/mark-16.png",
        "size": 16
      }
    ]
  },
  "commands": {
    "toggle-mode": {
      "suggested_key": {
        "default": "Ctrl+Alt+M",
        "linux": "Ctrl+Alt+M"
      },
      "description": "Send a 'toggle-mode' event"
    },
    "scroll-mark-down": {
      "suggested_key": {
        "default": "Ctrl+Alt+Down",
        "linux": "Ctrl+Alt+Down"
      },
      "description": "Send a 'scroll-mark-down' event"
    },
    "scroll-mark-up": {
      "suggested_key": {
        "default": "Ctrl+Alt+Up",
        "linux": "Ctrl+Alt+Up"
      },
      "description": "Send a 'scroll-mark-up' event"
    }
  }
}