I couldn't really understand what information is
stored inside the BufferView.offset_ref_ variable.
At a first glance, it would seem that anchor_ref_
stores the "paragraph offset" that is displayed from
the WorkArea top line, and offset_ref_ stores the
"pixel offset". Namely, the top WorkArea line of
pixels would display the offset_ref_-th line of
the anchor_ref_-th paragraph.
Even if I keep these two values in sync with the scrollbar,
it seems there are other variables that decide what pars
the workarea starts displaying from the top.
Moreover, what var decides how the gray text background
is cut at the end of the doc ?