The Logger Product adds the tag, so that DTML code may send messages directly to Zope's logging subsystem (as documented in docs/LOGGING.txt found at the root of your Zope2 installation). One use of this tag is to help debug complex DTML and ZSQL methods.
This product is known to work with versions of Zope between 2.1 and including 2.4.3. It should also continue to work in future versions of Zope.