Examine source code of Enable Selection

{
  "manifest_version": 2,
  "name": "enable-selection",
  "version": "1.7",
  "icons": {
    "60": "icons/select_60x60.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "selection.js"
      ],
      "css": [
        "selection.css"
      ],
      "all_frames": true
    }
  ]
}