If under Tools AutoCorrect Options, AutoFormat as You Type, the Border lines
box is checked, it you type ### and the press Enter, a border will be
created.
If at that point you press the backspace key, the border will be undone,
leaving the ###.
If you enter some other text, and the go back to the position immediately
following the border (that is at the beginning of the next line) and press
the backspace key, the border will be removed without leaving the ###.
If the Border lines box is not checked, a border will not be created by
pressing the Enter key after typing ###.
The above was determined through performing the steps mentioned, i.e. by
testing.
--
Hope this helps.
Please reply to the newsgroup unless you wish to avail yourself of my
services on a paid consulting basis.
Doug Robbins - Word MVP