This is how it works ...
When Cocoon generates the site, it crawls each document and gathers any new links to be processed. There is a special URI "linkmap" which is the map of the complete site.
This is utilised to have a special sitemap match "linkmap.validation-start.xml" which transforms the linkmap to have links ending in "*.validation.xml".
Cocoon has the ability to include extra URIs for processing. Add the line "linkmap.validation-start.xml" to a conf/uris.txt file. Then add the following line to the 'forrest.properties' configuration file:
This causes Cocoon to generate all the "*.validation.xml" validation report files.
After the 'forrest site' completes, Ant summarises all those reports into build/tmp/validation-reports.html and then removes all the individual reports.
See also http://forrest.apache.org/howto-dev.html#validate-intermediate