I checked this commit out, and failed to see how these low/high priority handlers work out in practice. I tried to
No tests failed. Is there any one patch so far that demonstrates why we need this? A unit test?
add with high priority == add to the beginning of the queue
This means that it doesn't matter with what priority we add the very first one.
In the future commits, InterestingLValueHandler HAVE TO BE before before DefaultExpressionHandler and there are tests that validate it. Actually this is the only place that I know that really cares about the order and that's why I needed to add priorities and the way for one handler to cancel all further handlers.
Does this answer your question?