Why I can't define android attributes in default namespace?

Question

Typically I have to write layout code like this:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="fill_parent" 
              android:layout_height="fill_parent" 
              android:orientation="vertical" />

I want to do something like this:

<LinearLayout xmlns="http://schemas.android.com/apk/res/android"
              layout_width="fill_parent" 
              layout_height="fill_parent" 
              orientation="vertical" >

But this code doesn't run properly. Why?

And second question: Why element namen are in CamelCase and attributes are in under_score?

Answer 1

XML default namespaces do not apply to attribute names. Hence, you always have to specify the namespace of an attribute, if it has one:

Default namespace declarations do not apply directly to attribute names; the interpretation of unprefixed attributes is determined by the element on which they appear.

So the real question is: Why did the Android designers define the element names without a namespace, putting only the attributes into the Android namespace?

As the document suggests, if the element names were in the Android namespace, then attribute names really wouldn't need their own namespace.