Examine source code of When2Meet Autofill

{
  "name": "When2Meet Autofill",
  "description": "Save and fill when2meet.com schedules",
  "version": "1.1",
  "manifest_version": 2,
  "permissions": [
    "storage",
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "/images/16icon.png",
      "32": "/images/32icon.png",
      "48": "/images/48icon.png",
      "128": "/images/128icon.png"
    }
  },
  "icons": {
    "16": "/images/16icon.png",
    "32": "/images/32icon.png",
    "48": "/images/48icon.png",
    "128": "/images/128icon.png"
  },
  "web_accessible_resources": [
    "fillPage.js"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.when2meet.com/*"
      ],
      "js": [
        "onload.js"
      ]
    }
  ]
}