[Oberon] SystemV - Viewer Scroll

[Tomas Kral]

Hi,

Observing text viewer scroll by `MM'. 

[1]
When scrolling down, a portion of
text is copied up `CopyBlock', vacant part is cleared at the bottom,
a new text is copied into `CopyPattern'.

[2]
When scrolling up, the whole viewer is cleared and redrawn by
`CopyPattern'.

I wish [2] behave similar to [1], possible? 
Looking for a hint as to where in the source text this could be
experimented with?

Many thanks.

-- 
Tomas Kral <thomas.kral at email.cz>