Integrated with modifications into trunk and 1.1 branch.
Allowed namespaces are:

• empty namespace
• http://www.w3.org/XML/1998/namespace
• http://www.w3.org/1999/xhtml
• http://www.w3.org/2000/svg
• http://www.w3.org/1998/Math/MathML

But this can be configureable.

only let the following namespace go through

• {}
• {http://www.w3.org/1999/xhtml}
• {http://www.w3.org/2000/svg}
• {http://www.w3.org/1998/Math/MathML}

list to put in the configuration of the component ? component is often overloaded... will be awfull to do
=> put this list hardcoded and allow overloading

Joined newest jars (compiled by Cedric Damioli for coherence with other cocoon jars).

I reopened this issue as it has not been integrated yet on both trunk and 1.1 branch.

Joined the HEAD patch file (contains the XHTMLSerializer and the release note) and the two dependencies.
The serializers block is to be included in the kernel libs, the charsets in the application template.

Added a new XHTML serializer, based on cocoon's XHTMLSerializer, which doesn't collapse most of the tags.
New jars were added to the kernel and to the application template, so make sure to add them to your project when upgrading.

Temporary workaround : created a new Serializer based on cocoon's XMLSerializer, specifying a new content handler which inherits from xalan's ToXMLStream, never collapsing empty elements.

Generating with this serializer and specifying it as the default serializer in the site workspace sitemap seems to work as expected.
However, setting is as the html serializer in the kernel's sitemap (used all over the CMS application) instead of cocoon's HTMLSerializer generates some unexpected effects : some characters seem to be output escaped.

I find that cocoon has a serializer block with a XHTMLSerializer but it does supports only textarea, script, style and meta.

I have just submitted a patch with a new xalan property for disabling empty element collapsing:
https://issues.apache.org/jira/browse/XALANJ-1906

Xalan collapse textarea whatever the transformation output method use.
Adding a comment is simply rendered as text in the textarea.

There two solutions :

• use a invisible space caracters like "Zero Width No-Break Space" (only in unicode) ;
• wrap the final OutputStream in a Writer for replacing "<textarea.?/>" with "<textarea></textarea>".

For weird spaces see:
http://en.wikipedia.org/wiki/Space_(punctuation)