The terminology is confusing, especially with me having come from Vim:
"horizontal" in this case means a vertical split, because they are stacked
horizontally.
My previous window layout put the body of the article below the summay,
which left a lot of whitespace to the right of my 272-column terminal. So I
went from
-------------------------
| S | T |
|-----------------------|
| A |
-------------------------
to
-------------------------
| S | |
|-----------| A |
| T | |
-------------------------.
This also lays out nicely with BBDB:
------------------------- -------------------------
| S | T | | S | A |
|-----------------------| => |-----------|-----------|
| A | | T | B |
|-----------------------| -------------------------
| B |
-------------------------
Mike Gerwitz