The current Zope TAL code is old from 2004ish. It should be brought up
to date with the current page template code. I assume there are performance
and possibly security updates in there as well.

The current TAL code we have was modified from the distribution code when it was
made a part of Roundup. Richard didn't remember what changes were made but there
are some notes in the files. For example PageTemplates/Expressions.py says:

   # Modified for Roundup:
   #
   # 1. removed all Zope-specific code (doesn't even try to import that stuff now)
   # 2. removed all Acquisition
   # 3. removed blocking of leading-underscore URL components


Most likely this work needs to be done on a branch since I think all three of these
components need to be upgraded together. That's also why this is a single issue.
If it turns out they can be upgraded piecemeal create tickets for each part.

Also try to get the testing suite built for this as we go. Maybe tal/page templates has a
test suite we can use.