Chrome performance tool - What's going in the long task after the html has downloaded but before the HTML is parsed?

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I am trying to learn how to use the Chrome performance profiler to better optimise my applications but am finding it difficult to reason about the results I receive as they are a bit vague.

I have an application that has a small amount of HTML on it and running it in incognito mode.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  Hi
</body>
</html>

enter image description here

I have set a cache control header to attempt to cache the index page in the browser to eliminate network overhead and focus only on parse/rendering however it still makes a request to the server.

Even still, the 2ms value only covers a small portion shown in the performance tools which I assume is network transfer.

enter image description here

What is this "task" doing and why is it taking so long?

enter image description here

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