Examine source code of a2er

{
  "name": "a2er",
  "version": "1.2",
  "manifest_version": 2,
  "author": "Sebastian Schicho",
  "description": "Replace all words ending with `a` to end with `er`.",
  "icons": {
    "32": "icons/er32.png",
    "48": "icons/er48.png",
    "96": "icons/er96.png",
    "128": "icons/er128.png"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "browser_action": {
    "default_icon": {
      "32": "icons/er32.png",
      "48": "icons/er48.png",
      "96": "icons/er96.png",
      "128": "icons/er128.png"
    },
    "default_title": "a -> er"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "a2er.js"
      ],
      "run_at": "document_start"
    }
  ],
  "commands": {
    "parse_page_now": {
      "suggested_key": {
        "default": "Alt+K",
        "windows": "Alt+K"
      },
      "description": "Manually trigger the conversion to `er`."
    }
  }
}