TL;DR: The motivation for the change is focused on guidance around
whitespace; the original intent of the requirement, and indeed the
whole document, is around stability of the interpretation of
identifiers and pattern-based syntax. The specific guidance about
whitespace that is being added does not fall within the scope
described by the summary of the document. The applicability of the
formulation with Pattern_Syntax to non-pattern-based languages is not
established. The assumed nature of "whitespace" is also not clear.

On Fri, May 20, 2022 at 11:52 PM Hubert Tong
<hubert.reinterpretcast_at_[hidden]> wrote:
>

> Note: The characters not in the basic character set and not part of an
> identifier won't need to be Pattern_Syntax under the profile. We error
> on those outside of string/character literals.

Hmm. I am not sure for such characters what having them as
Pattern_Syntax or not implies.

I'm pretty sure we don't need them to be Pattern_Syntax in the
profile, but having the ones that are Pattern_Syntax in the UCD remain
Pattern_Syntax is probably right too.

We treat them all the same anyway, and we already retain the ability
to use them for whatever purpose outside of literals in the future
without breaking currently-conforming programs.

It's not like we automatically accept the set of characters neither in
Pattern_Syntax and Pattern_White_Space (unlike the assumed behaviour
for pattern languages).

We already succeed in the original intent of the requirement insofar
as character sets are concerned: Currently-conforming programs would
not change meaning because of future choices to use new characters for
syntactic purposes outside of literals.

I do not believe the intent of the new change (to apply some
whitespace-related guidance to general programming languages) falls
within the intent of the original requirement (to keep valid patterns
stable). It may be more appropriate to formulate a new, separate
requirement to implement the intent of the new change (which is mostly
restricted to Pattern_White_Space concerns and does not need to bring
Pattern_Syntax into it).

The document should also make its assumptions about "whitespace"
clear: Is all whitespace expected to be treated equivalently, or is
that specifically not assumed?

Finally, the update to the document does not make appropriate updates
to reflect expansions to its scope (at the document level in its title
and summary, and in the heading given for the "Pattern Syntax"
section).