> But I suggest that modes preclude many and perhaps most parallel implementation methods,
> which has helped XML adroitly avoid most of the improvements to CPUs in the
> last 25 years. And a technology in that situation is not in a healthy place.

XML and SGML don't have escape characters, owing to their IBM as
opposed to Unix tradition also showing in its commenting syntax
(technically, SGML has MSOCHAR, MSICHAR, MSSCHAR but these are not
assigned in the default concrete syntax). Verbatim inclusion of markup
delimiters is performed through entity references (eg <). So isn't
SGML/XML already doing what you're postulating ie avoiding the need
for arbitrary lookback in assessing whether a given escape isn't
escaped itself etc etc, which would be necessary with backslash
escapes in the Unix way, and which btw can't also be captured by
regexpes, or only in a bounded way?