Examine source code of Grammar Checker and Writing Assistant by Sapling

{
  "manifest_version": 2,
  "name": "Sapling Grammar Checker and Writing Assistant",
  "short_name": "Sapling",
  "description": "Improve your writing with a spell + grammar checker and writing suggestions.",
  "version": "2.5.1.0",
  "author": "sapling.ai",
  "icons": {
    "32": "assets/sapling-32x32.png",
    "48": "assets/sapling-48x48.png",
    "128": "assets/sapling-128x128.png",
    "176": "assets/sapling-176x176.png"
  },
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "browser_action": {
    "default_icon": {
      "40": "assets/sapling-40x40.png"
    },
    "default_title": "Sapling",
    "default_popup": "generated/popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "addon@sapling.ai",
      "strict_min_version": "42.0"
    }
  },
  "permissions": [
    "alarms",
    "identity",
    "identity.email",
    "storage",
    "activeTab",
    "tabs",
    "<all_urls>",
    "clipboardWrite",
    "clipboardRead",
    "webNavigation"
  ],
  "background": {
    "scripts": [
      "generated/jquery-3.5.1.min.js",
      "generated/background-bundle.js"
    ],
    "persistent": true
  },
  "commands": {
    "accept-all-edits": {
      "suggested_key": {
        "default": "Alt+O",
        "mac": "MacCtrl+O"
      },
      "description": "Accept all edit suggestions"
    },
    "accept-current-sentence-edits": {
      "suggested_key": {
        "default": "Alt+I",
        "mac": "MacCtrl+I"
      },
      "description": "Accept edit suggestions in current sentence"
    },
    "toggle-snippet-controls": {
      "suggested_key": {
        "default": "Alt+L",
        "mac": "MacCtrl+L"
      },
      "description": "Launch snippet selector"
    },
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Alt+S",
        "mac": "MacCtrl+S"
      }
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://sapling.ai/no_declarative_injections"
      ],
      "all_frames": true,
      "css": [
        "assets/sapling.css",
        "generated/icomoon.css"
      ],
      "js": [
        "generated/jquery-3.5.1.min.js",
        "generated/main-bundle.js"
      ],
      "match_about_blank": true
    },
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "scripts/gmail-injector.js"
      ],
      "run_at": "document_start"
    }
  ],
  "externally_connectable": {
    "matches": [
      "https://mail.google.com/*"
    ]
  },
  "web_accessible_resources": [
    "assets/*",
    "generated/gmail-module.js",
    "generated/gmail-listener.js"
  ]
}