There is an internal flag on each subfile record.
When the user changes the record the flag is set.
When the program reads the record, usually with the READC, the flag is turned off.
If you want the flag on after that read – set the SFLNXTCHG on and update the subfile record.
This is often used when the program needs to make two passes through the changes
1. edit the requests – are they all valid
2. process the requests
In pass #1 there would be a READC loop which checked each request , processed errors, set the SFLNXTCHG on and updated each changed record
if all records passed pass #1
pass #2 would use the READC to acquire and process each changed record.