Why we use non-existing XMLNS urls?

Question

In the XML heads, I have seen that a lot of xmlns values do not exist as their URLs as mentioned.

Why we we still use non-existing urls there? Let us see one xml sample from Android Studio's layout file.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
...

In the above example, the URL http://schemas.android.com/apk/res/android does not exist. Many other urls used in XMLs in similar way do not exist at all.

Answer 1

Those are not URLs but rather URIs, they only identify a ressource rather than locating it. As identifiers, they should be unique and try to describe the ressource, but there is no need for them to provide the ressource.