Examine source code of PencilToggler

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "PencilToggler",
  "version": "0.0.0.1",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "description": "Use custom shortcut to toggle the pencil in the New York Times Crossword desktop app.",
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.nytimes.com/*"
      ],
      "js": [
        "autorun.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "commands": {
    "toggle-pencil": {
      "suggested_key": {
        "default": "Ctrl+0",
        "mac": "Command+0"
      },
      "description": "Toggle pencil"
    }
  },
  "icons": {
    "16": "images/16.png",
    "32": "images/32.png",
    "48": "images/48.png",
    "128": "images/128.png"
  },
  "manifest_version": 2
}