Enhance keyboard scrolling

Dear,
I would like to suggest the following enhancement:
-PgDown PgUp:
Currently they scroll the score a full page, whatever the proportion of the page you see on screen.
It would be very convenient if they would scroll only the visible size of the page (as do lot of softwares MS-Word, Acrobat Reader, Foxit reader, Nitro, ...)
-ArrowUp, Down, Left, Right
When nothing is selected, they should scroll the page a little bit (again as do lot of softwares)
With these two combined, you would be able to navigate using the keyboard only, which is not possible today.
Thanks for reading