After an error occurs, if $ZYERROR is set to a valid entryref that exists in the current environment, GT.M invokes the routine at that entryref with an implicit DO before returning control to M code specified by $ZTRAP or device EXCEPTION. It is intended that the code invoked by $ZYERROR use the value of $ZSTATUS to select or construct a value to which it SETs $ZERROR.

If $ZYERROR is empty, $ZYERROR="unprocessed $ZERROR, see $ZSTATUS".

If there is a problem with the content of $ZYERROR or if the execution of the code it invokes, GT.M sets $ZERROR=$ZSTATUS for the secondary error and terminates the attempt to use $ZYERROR. During code evoked by $ZYERROR, the value of $ZERROR is the empty string.