The only outright omission I see in the RSS 2.0 specification is that it
does not mention the namespace to be used for the elements described in
the document.

In cases where there is lack of precision in a specification, people
look to other sources for guidance. In this case, two such sources are
the newsfeed for scripting news and the radio news aggregator as
effectivly "reference implemenations".

In prior versions of RSS, the elements were for all practical purposes
in a namespace named "". Now the scripting news feed places these
elements into a namespace named "http://backend.userland.com/rss2". I
suspect that this specification would get wider adoption if this were in
a vendor neutral namespace such as "http://purl.org/rss/2.0/".

Based on experimentation by Jon Udell, it appears that the radio news
aggregator does not support explicit qualification of the channel
element in the "http://backend.userland.com/rss2" namespace via a
prefix. At this time this issue appears to be limited to the channel
element.

Net: no mention of the namespace introduced in 2.0, coupled with
incomplete support of the same, tends to promote confusion.

- Sam Ruby