bug#33887: 26.1; Emacs hangs for several seconds when going to the end of an XML file in nXML mode

[Fernando Jascovich]

Hi everyone, this is my first email to bug-gnu-emacs, so please let me
know if I am making some mistake.
For no special reason, I took this bug in order to start to know  emacs'
code.
Following and confirming the details of the bug, I found that indeed the
performance issue is introduced at commit 0055190174, but not beacuse
the introduction of `sgml-syntax-propertize-inside`.
The problem is with the last rule:
```
("\"" (0 (if (prog1 (zerop (car (syntax-ppss (match-beginning 0))))
                    (goto-char (match-end 0)))
                  (string-to-syntax ".")))
```
I can't see the real effect of this rule, I tested xml parsing without
this rule and it works fine, marking double quotes inside tags as
expected without this performance issue.
Do we need to target double quotes outside tags explicitly?

-- 
Fernando Jascovich
developer
m: +54 9 3548 63 9833
github: https://github.com/fernando-jascovich/
linkedin: https://www.linkedin.com/in/fernandojascovich/