lxml etree question

[Jim]

Hello,  I wonder if someone knows about lxml.etree and namespaces?

I want to build an ElementTree where some of the sub-elements have
attributes that serialize this way.

  <comment xml:lang='de'>..</comment>

I've tried just comment_elet.set('xml:lang','de') and it didn't like
that at all (although it takes comment_elet.set('auth:id','jones')
just fine).  I've also spelunked the docs and googled but have not hit
on the right invocation.  If someone knows, I'd be grateful.

Jim