Why Android Use Separate Xmlns For Contraintlayout

I'm little confused about ConstraintLayout in Android. I was learning about it and first thing I get confused about it why android use separate xml namespace for it? xmlns:app='htt

Solution 1:

ConstraintLayout is part of Layout then why google didn't added it in the old namespace?

That is reserved for platform-defined attributes. ConstraintLayout is from a library, not from the platform.

and why android required to write full qualified name in XML? android.support.constraint.ConstraintLayout why not just ConstraintLayout?

Android only knows to look in a couple of platform-defined packages for views using the shorthand, bare-class-name-only notation. android.support.constraint is from a library, not the platform.