&gt; It communicates exactly what the browser is<p>This is true, which is not particularly useful when deciding if a feature is available. Using the user agent to make this decision incorrectly assumes that all user agents of a particular browser+version all support exactly the same set of features. This is obviously not true.<p>The user agent may be meaningful[1], but the meaning that it communicates isn&#x27;t feature data.<p>[1] If you take the header at it&#x27;s word; as the bug being discussed demonstrates, user ages may be lying.