chromium/chrome/test/data/extensions/blocked_actions/content_scripts/manifest.json

{
  "name": "Blocked Actions Doc Start",
  "description": "An extension that wants to run at document start on all urls",
  "version": "0.1",
  "manifest_version": 3,
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "script.js"
      ]
    }
  ]
}