Correct. I have found the error in a custom template. This no longer works with Chameleon/zope.tales in Zope 4.4:
tal:omit-tag="True"
It should be:
tal:omit-tag="python:True"
Also, in a different template I used
tal:repeat="slide slides"
and then in a Python expression I used:
repeat.slide.start()
That gives RuntimeError: 'bool' object is not callable.
Solution is to use repeat.slide.start, but that probably fails with earlier chameleon. So I rewrote it to a path expression repeat/slide/start.
So likely various templates in add-on code need changes, as others have already seen. And maybe some core code where tests are missing.
So we might need to revert to Zope 4.3. But in the 4.4 changelog I see: " * Fix incompatiblities with Archetypes". Ah, but I reported those incompatibilities in March, and they were caused by the tales/chameleon/engine changes in 4.4. So for that part, 4.3 should be fine.
I am on the fence on this one: revert to Zope 4.3, or wait until the incompatibilities have been solved in a newer Zope 4.4 / chameleon release.
Note: individual templates are probably easy to fix, but for the first example in this comment it took me a long time to find which template it was. (Caching, even in development mode, and a jbot override did not help...)