the following (valid) html:
<!DOCTYPE html>
<html>
<title>Hoi</title>
<script async defer src=\"http://foo.com/bar.js\"></script>
<h1>yo</h1>
becomes this:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"><script>window.FactlinkProxiedUri = "http://www.example.org/foo?bar=baz";</script><script></script>defer
src="http://localhost:8000/lib/dist/factlink_loader.js?o=proxy"
onload="__internalFactlinkState('proxyLoaded')"
></html>