Alt text and media types for preformatted text

[Sean Conner]

It was thus said that the Great Thomas Frohwein once stated:
> On Mon, Mar 01, 2021 at 07:48:56PM -0500, Sean Conner wrote:
> > It was thus said that the Great Nathan Galt once stated:
> > > 
> > > 
> > > On Mon, Mar 1, 2021, at 1:24 PM, Sean Conner wrote:
> > > > 
> > > >   While I would like to disallow control codes in the specification, that
> > > > might be too big of a change, and *will* affect some sites, but adding
> > > > verbiage that discourages it can be added.
> > >
> > > Perhaps this is the wrong way to frame this, but you're prioritizing
> > > backwards compatibility on a pre-1.0-spec to support an unintended hack
> > > that has security issues?
> > 
> >   If I recall, escape codes where *never* in any of the specifications, just
> > an oversight when documenting the format (aka "loophole").  
> > 
> > > If I had control codes on my capsule, I'd grumble a bit, sure, but I'd
> > > remove them. I'm not sure it's worth it to shield the tiny handful of
> > > **current** capsule operators from some search-and-delete work compared to
> > > all the future client implementors who'll face at least some pressure to
> > > implement color support (and, if they're actual terminal applications,
> > > open their users to keyboard-reset exploits).
> > 
> >   I'd ban control codes in a heartbeat (except for HTAB, CR and LF as
> > stated), but I'm not sure how popular that decision would be.
> 
> I would support it. I think this step would work best if coupled with
> best practices or code example for clients to identify and ideally
> remove or warn/error if encountered. The client that I'm working on is
> ncurses-based and doesn't support escape codes for that reason. But
> maybe a visible difference to text without escape code would be enough
> to weed out existing escape code hacks. A simple way would be to guide
> clients to how to print the escape codes as plain text rather than
> processing them. Could probably come up with a simple regex/tr to get
> started...

  I posted a BNF format for the C1 control codes here:

	https://mailing-list-archive.gemi.dev/www/2020/000390.html

  For the C0 set, just filter out anything between character 0 and 31, with
the exception of HTAB (9), LF (10) and CR (13).

  -spc