Examine source code of Clean Number

{
  "name": "Clean Number",
  "description": "Clean Number strips non numbers and spaces from text for digit only copy and paste.",
  "version": "2023.1",
  "manifest_version": 3,
  "homepage_url": "https://bizpep.com/ext/cn/",
  "icons": {
    "128": "128.png"
  },
  "action": {
    "default_title": "Click to Clean Number",
    "default_icon": {
      "128": "128.png"
    }
  },
  "permissions": [
    "activeTab",
    "scripting"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "cn@bizpep.com"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}