SYSTEM.MASTER_BLOCK
This system variable works with its companion SYSTEM.COORDINATION_OPERATION to help an On-Clear-Details trigger determine what type of coordination-causing operation fired the trigger, and on which master block of a master/detail relation.
The values of the two system variables remain constant throughout the clearing phase of any block synchronization. SYSTEM.MASTER_BLOCK represents the name of the driving master block, and SYSTEM_COORDINATION_OPERATION represents the coordination-causing event that occurred on the master block.
Please see the reference topic for SYSTEM.COORDINATION_OPERATION for more information.