bug#61514: 30.0.50; sadistically long xml line hangs emacs

[Eli Zaretskii]

> Date: Sat, 18 Feb 2023 09:06:25 -0800 (PST)
> From: "Mark A. Hershberger" <mah@nichework.com>
> Cc: 61514@debbugs.gnu.org
> 
> Eli writes:
> > The problem is in the combination of nxml-mode and some subtle
> > bug/misfeature in our regexp routines.
> 
> Thank you for your work in tracking this down.
> 
> That regex looks pretty awful.

Yep.  And coupled with quadratic (or worse?) behavior of our
backtracking regexp engine, it's a killer.