+++ vitaly [May 02 15 21:05 ]:
As workaround we could require at least 2 chars for setex.
As others have also pointed out, there is a legitimate use for these
in things like
A
-
Also, since existing implementations only require one character in the
setext header line, there may be many existing documents that lazily
use just one character, e.g.
My title
-
and these would break with the change you propose.