When I scroll synchronized down to the position where one list ends, I know that the rest of the other is "stand-alone". May it be 2 lines or 20 pages. And I can handle it appropriate.
If you want a special handling of scrolling in this situation: please do it symmetric, i.e. when scrolling synchronized *up*, and one list ends - what do now?
My expectation is, that "some differences" in the lists will be there from time to time:
- one time maybe some at the top
- one time maybe some at the bottom
- and several times some in between.
So top and bottom just are a minority of positions for differences - and I think I will be able to handle them...
OK - the lists could be automatically adjusted, i.e. identical files in both lists could be shown "side by side", while at the position of "missing" files there could be a gap. (This is the escalation, when scrolling "with respect to list-states".)
And files with same name, but different attributes (length, dates, ...) could be marked in different colors...
...but I don't really want to request that
So I think, the user himself can be responsible for aligning both list - may it be down, or may it be up.
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