The activation of $ETRAP and $ZTRAP are the same, however there are a number of differences in their subsequent behavior.

For subsequent errors the then current $ZTRAP is invoked, while with $ETRAP, behavior is controlled by the state of $ECODE. This means that when using $ZTRAP, it is important to change $ZTRAP, possibly to the empty string, at the beginning of the action in order to protect against recursion caused by any errors in $ZTRAP itself or in the code it invokes.

If there is no explicit or implicit GOTO or ZGOTO in the action, once a $ZTRAP action completes, execution resumes at the beginning of the line where the error occurred, while once a $ETRAP action completes, there is an implicit QUIT. This means that $ZTRAP actions that are not intended to permit a successful retry of the failing code should contain a GOTO, or more typically a ZGOTO. In contrast, $ETRAP actions that are intended to cause a retry must explicitly reinvoke the code where the error occurred.

For QUITs from the level at which an error occurred, $ZTRAP has no effect, where $ETRAP behavior is controlled by the state of $ECODE. This means that to invoke an error handler nested at the lower level, $ZTRAP actions need to use an explicit ZMESSAGE command, while $ETRAP does such invocations implicitly unless $ECODE is SET to the empty string.