I think you’ll have difficulty implementing a Position To in a Load All subfile. How will you identify which record in the subfile to position to? The subfile only allows RRN access if you want to chain to or position to a specific record.
To do it you would need to identify the relative record number of the record you want to position to.
A dirty method would be to record in an array or multiple-occurrence data structure where parts of the position to key change. For example, if you want to position on say Surname, you have a 28 element single character array.
In element 1 you store the RRN of the first subfile record with a surname beginning with A, in element 2 the RRN for a surname beginning with B, etc through to element 6 for Z.
In 27 you store the first RRN with a non-alphanumeric first character in the surname and in 28 the first RRN with a surname beginning with a digit.
When you do your position to, you complete the Position-To field and press Enter or a Fn key. The program then takes the first character and finds the corresponding element to pick up the RRN. You then chain to the RRN and read through until you find a match on the surname or a surname that is greater than the position to. That gives you your positioning RRN which you can use for the top line of the subfile.
It’s messy and depending on the number of records could be unworkable. You can expand the concept by recording changes of RRN on say the first three characters of the position to field instead.
The best way to handle a position to is to use a single page if you want to allow paging up/rolling back through the subfile or an expanding subfile if you don’t mind not being able to page up/roll back.
Using Page Up and Page Down in a Load All subfile makes no difference, the system still handles all of the paging. By using a Position To you handle the positioning to the appropriate RRN and tell the subfile which record to position to. The paging is handled automatically.
Hope that helps
All the best