Examine source code of Cards++

{
  "name": "Cards++",
  "description": "Display max bid, min ask and market value of the cards in your deck.",
  "version": "1.0",
  "manifest_version": 2,
  "content_scripts": [
    {
      "matches": [
        "https://*.nationstates.net/page=deck*",
        "https://*.nationstates.net/nation=*/page=deck*"
      ],
      "js": [
        "cards.js"
      ]
    }
  ],
  "icons": {
    "16": "/images/cards16.png",
    "32": "/images/cards32.png",
    "48": "/images/cards48.png",
    "128": "/images/cards128.png"
  }
}