This is a file with no HTML tags at all.

Browsers are incredibly forgiving. Even though this file has no DOCTYPE, no html element, no head, no body, and no tags of any kind, the browser will still render it as a web page. Open your Developer Tools (F12) and look at the Elements panel. You will see that the browser created a full DOM tree: html, head, and body elements were all generated automatically.

This behavior is defined by the HTML specification's error-recovery algorithm. The parser is required to handle any input gracefully, constructing a valid DOM even from completely unstructured text.

Of course, you should never rely on this. Always write proper HTML with a DOCTYPE, character encoding, and a valid document structure. This file exists only to demonstrate the browser's error tolerance.

Try running this file through the W3C Validator at https://validator.w3.org/ and observe the errors it reports.