bear scripsit:

> The particular example I'm thinking of is splitting strings
> between base codepoint and combining codepoint. You get two
> substrings, and the second one is syntactically invalid.

Please point to a place in the Unicode Standard where any sequence
of Unicode scalar values is said to be "syntactically invalid".

> If you print the first substring and then the second, the
> combining codepoint is usually printed as though it modified
> a space character that isn't actually there.

That's one possibility; it can also be rendered on top of
a dotted-circle, which is what is done in the Unicode charts.
In any case, glyph rendering is not part of the Standard.

> If something
> normalizes the substrings first, the space may actually be
> added, although it wasn't present in the original string.

That turns out not to be the case.  The normalized form of
a string consisting of one combining character is itself.

> Gah.  Encodings, normalization forms, endianness, and all the
> rest of it.  When you want to write a "character" any of a dozen
> things can happen.

Blurring significant distinctions that have taken a long time to
nail down isn't very conducive to clear thinking.

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