This is an inbuilt function function provided by PPWIZARD.
The StackPush() and StackPop() routines can be used to store and restore information. Another major use is to validate steps that must be performed in pairs. When a build is completed all pushed items on all stacks must have been popped or the items on the stack are listed and the build fails.
For every StackPush() operation there must be a corresponding StackPop().
Note that the "#PUSH and #POP commands use this mechanism for storage.
The function takes one parameter as follows:
An error is generated if there is nothing on the stack otherwise the value is returned.