Stripping namespace from DocBook 5 document

When I "compile" my DocBook file from within emacs's nxml mode:

    -*- mode: compilation; default-directory: "~/public_html--Hayek.name/" -*-
    Compilation started at Thu Jul 19 20:58:29

    make -k html
    env XML_CATALOG_FILES=/etc/xml/catalog \
        xsltproc \
            --output book.html \
            _xsl/html--docbook.xsl \
            book.xml
    Stripping namespace from DocBook 5 document.
    WARNING: cannot add @xml:base to node set root element.  Relative paths may not work.
    Processing stripped document.

    Compilation finished at Thu Jul 19 20:58:31

I'm getting a few strange messages:

    Stripping namespace from DocBook 5 document.
    WARNING: cannot add @xml:base to node set root element.  Relative paths may not work.
    Processing stripped document.

This is how my document starts:

    <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML 5.0CR4//EN" "http://www.oasis-open.org/docbook/xml/5.0CR4/dtd/docbook.dtd" >

    <article version="5.0" class="techreport" xmlns="http://docbook.org/ns/docbook" xmlns:xl="http://www.w3.org/1999/xlink">

I am sure I did not get those messages, when I used DocBook 4.5,
only when I migrated to DocBook 5, I introduced "that namespace stuff"
and I started getting these messages.

Maybe I haven't gotten it entirely right ...


How serious shall I take those 3 messages?
And what impact do they really have?
Can I get rid of a few of them?

I mean, I only introduced "that namespace stuff", so that nxml mode wouldn't mourn at me
and so that the document complies to what I found at

    http://www.oasis-open.org/docbook/specs/docbook-5.0b6-spec-wd-01.html

which looks to me (according to http://www.oasis-open.org/docbook/specs/)
like the latest document on DocBook 5.