On 23-01-23 12:47PM, Christian Weisgerber wrote:
> On 2023-01-23, Mark Jamsek <mark@jamsek.com> wrote:
> 
> > Oh whoops, I've been doing it wrong! I always thought it was [1,80] not
> > [1,80)  :)
> 
> There was a historical reason to stay clear of the 80th column.
> 
> A traditional video terminal had 80 columns.  Let's say you write
> 79 characters from the start of the line.  Now your cursor is on
> the final column.  Then you write another character.  What happens
> next?
> 
> In early video terminals, the cursor would wrap around and advance
> to the first column of the next line.  If you then wrote a newline
> to move one line down, the cursor would be _two_ lines down.  Oops.
> Also, if you wrote to the final column of the bottommost line, the
> cursor would wrap around and the screen would scroll up one line.
> Which means you could never fill the screen completely.
> 
> Some terminals introduced a modified behavior: When you write to
> the final column of a line, the cursor stays there.  It will only
> wrap around if you write one more character; effectively the cursor
> position jumps by two characters.  The termcap(5) property "xn"
> marks a terminal with this behavior.  All DEC terminal starting
> from the VT100 had it.  So does xterm, etc.
> 
> I think the last terminal I ran into that didn't have this was some
> earlier iteration of the FreeBSD console, but we're a few rewrites
> beyond that, too.  So, yeah, I don't think it's a concern nowadays.
> 
> Anyway, that's the historical reason why people tended to avoid
> writing to the final column.

That's super interesting! And makes a lot of sense for treating the 80
column limit as exclusive. Thanks for the history lesson :)

Obviously less of a concern nowadays, but the etiology of these practices
are always informative, and, unsurprisingly, rarely arbitrary.

I've moved my column marker back one; I've treated that mark as
inclusive for too long to change, so by moving it I can continue doing
so while avoiding column 80 :)

-- 
Mark Jamsek <fnc.bsdbox.org>
GPG: F2FF 13DE 6A06 C471 CA80  E6E2 2930 DC66 86EE CF68