chromium/chrome/test/data/web_app_file_handling/basic_app_manifest.json

{
  "short_name": "file editor",
  "name": "super duper file editor",
  "icons": [
    {
      "src": "icon128.png",
      "sizes": "144x144"
    }
  ],
  "start_url": "icons_app.html",
  "display": "standalone",
  "file_handlers": [
    {
      "action": "icons_app_load.html",
      "name": "Plain Text!",
      "accept": {
        "text/plain": [".txt", ".text"]
      },
      "launch-type": "single-client"
    },
    {
      "action": "icons_app_load.html",
      "name": "spreadsheet",
      "accept": {
        "text/csv": [".csv"],
        "application/x-spreadsheet": [".sps"]
      },
      "launch-type": "multiple-clients"
    }
  ]
}