Window focus on desk/page change?

Configuration General Questions
11

It works well for GoToPage because of the universal variable $0 $1
GotoPage $0 $1, but not for WindowId. It gives a wrong ID number by adding the page numbers (11 digits instead of 9 digits).

Example window focus on Page 1 0
Wrong output:
WindowId 100x6002575 Focus

I tested on FvwmConsole, this works:
WindowId 0x6002575 Focus

Limited SOLUTION with separate variables for Page and ID:

+ I Current InfoStoreAdd lastFocusPage $[page.nx] $[page.ny]
+ I Current InfoStoreAdd FocusID $[w.id]
+ I GotoPage $0 $1
+ I WindowId $[infostore.FocusID] Focus

Best SOLUTION would be with universal variables $0 $1 $2 but something is missing with $2.

+ I Current InfoStoreAdd lastFocusPage $[page.nx] $[page.ny] $[w.id]
+ I GotoPage $0 $1
+ I WindowId $2 Focus

Any solution for WindowId $2 Focus ???