Events handled parameter must be var

[f4n0]

Happens a lot, even Microsoft has made a mistake like that.
if the Event signature, contains a parameter called "Handled" must be passed by var

[Arthurvdv]

..or IsHandled. But do we really want to hardcode this based on the name?

There are more cases, like for example a temporary table should also passed by var.

Just thinking at loud here; maybe an other way around is all event publisher with “OnBefore” in the name should pass all variables as var?

[f4n0]

well, a rule like:
If is an event, if the parameter is Boolean, if the parameter name contains "handled" then 99% need to be var