Unicode "no-op" Character?

[Sławomir Osipiuk via Unicode]

That's the key to the no-op idea. The no-op character could not ever be
assumed to survive interchange with another process. It'd be canonically
equivalent to the absence of character. It could be added or removed at any
position by a Unicode-conformant process. A program could wipe all the
no-ops from a string it has received, and insert its own for its own
purposes. (In fact, it should wipe the old ones so as not to confuse
itself.) It's "another process's discardable junk" unless known,
internally-only, to be meaningful at a particular stage.

While all the various (non)joiners/ignorables are interesting, none of them
have this property.

In fact, that might be the best description: It's not just an "ignorable",
it's a "discardable". Unicode doesn't have that, does it?

-----Original Message-----
From: Unicode [mailto:unicode-bounces at unicode.org] On Behalf Of Richard
Wordingham via Unicode
Sent: Saturday, June 22, 2019 20:59
To: unicode at unicode.org
Cc: Shawn Steele
Subject: Re: Unicode "no-op" Character?

If they're conveying an invisible message, one would have to strip out
original ZWNBSP/WJ/ZWSP that didn't affect line-breaking.  The weak
point is that that assumes that line-break opportunities are
well-defined.  For example, they aren't for SE Asian text.

Richard.