[tex-k] Why is B952. "Don't allow implicit left brace after |#| (Udo Wermuth). @476" considered a bug?

ud.usenetcorrespondence at web.de ud.usenetcorrespondence at web.de
Sat Feb 27 16:31:24 CET 2021

I just read at <https://tex.stackexchange.com/q/581118> about about
the bugs fixed in TeX, version 3.141592653.

Some questions:

About B952: This is attributed to Udo Wermuth, 20 May 2020.

I explained the behavior now subsumed as B952 already in 2018 under
"There is an edge thing" in my answer to "How does TeX look for
delimited arguments", <https://tex.stackexchange.com/a/438600>.

Before that I mentioned it in usenet.

Since I very much appreciate, and often use, the possibility
associated with this so-called bug of using any control sequence token
as an argument delimiter that is not removed, it would never have
occurred to me to think this was a bug. (Seems now this nice feature
is destroyed. (At the time of defining the macro in question the
control sequence token must be an implicit hash. At the time of
expanding the macro in question the control sequence in question
can be redefined to be something else.)

Not mentioning this possibility I thought was at best a sloppiness
in the TeXbook.

With many things that I have raised over the years and found
inconsistent with the description in TeXBook I have been told by
the luminaries at comp.text.tex/de.comp.text.tex/
TeX LaTeX Stack Exchange that they make sense and are intentional
and therefore should not be seen as bugs.

My question is:

What are the exact conditions under which things that deviate
from the behavior described in the TeXbook can be considered bugs?

I ask this in particular because in the preface of the TeXbook
the "technique of deliberate lying" is praised a means of easing
up understanding ideas (, which I doubt, but that's just my humble

So it is not necessarily clear when a deviation from the behavior
described in the TeXbook or a behavior just not mentioned in the
TeXbook actually constitutes a "bug" and when one has merely
uncovered another of these "deliberate lies", which could, after
all, also consist of deliberate non-disclosure.

Ulrich Diez

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