MachineFlags driver used to store values in a variable and which you can use across the system.
If you want to save a value in a "variable" you can use the MachineFlags driver.
MachineFlags can be added in the Virtual node.
After adding the MachineFlags node you can add your flag nodes.
After adding a Flag node you can set some values in the property grid on the left.
Save & reload your configuration and use your defined flag.