Examine source code of Save Text to File

{
  "name": "Save Text to File",
  "description": "Save highlighted text to a file on the computer.",
  "version": "4.3.1",
  "applications": {
    "gecko": {
      "id": "{1f0987e3-2483-44b9-81d3-22bb4c83374e}",
      "strict_min_version": "58.0"
    }
  },
  "permissions": [
    "contextMenus",
    "downloads",
    "storage",
    "notifications",
    "activeTab",
    "nativeMessaging"
  ],
  "background": {
    "scripts": [
      "backgroundScript.js"
    ]
  },
  "manifest_version": 2,
  "icons": {
    "64": "images/ico.png"
  },
  "options_ui": {
    "page": "options.html",
    "chrome_style": true
  },
  "commands": {
    "save-text-to-file": {
      "suggested_key": {
        "default": "Ctrl+Shift+Y"
      },
      "description": "Saves the selected text from the active tab to a file."
    }
  }
}