External namespaces

Hi all,

In the Glabels documentation, I want to use the following <span> tag to define some strings as not to translate:

<span its:translate="no">radius</span>

This is recommended in the Mallard documentation. But the appropriate strings remain as translatable, when I create the *.pot template with xml2po. The string appears as follows:

#: C/mancreate.page:314(span) C/mancreate.page:353(span)
#: C/mancreate.page:469(span)
msgid "radius"

In other cases, when I have a string with is mixed from a <span> with additional content:

<title><span its:translate="no">Label-cd</span> Node</title>

then I get the following po string:

#: C/mancreate.page:336(title)
msgid "<span translate=\"no\">Label-cd</span> Node"
While opening the manual with "yelp ./", a lot error messages appear, such as this:

/home/mario/GNOME-Git/glabels/help/C/mancreate.page:592: namespace error : Namespace prefix its for translate on span is not defined
   <p><span its:translate="no">Layout</span> Parameters</p>

For reference, please have a look at this file:

http://git.gnome.org/browse/glabels/plain/help/C/mancreate.page

Seems to be I have to supply the definition for the "its:" anywhere. How could I do this, and what I have to write? 
Thanks in advance for any explanations.

Best Regards,
Mario