Zero-width non joiner vs. zero width space?

[Phssthpok]

If I have a list of items separated by slashes, first/second/third, I want to be able to allow line breaks after a slash. The zero-width space and zero-width non-joiner characters both seem like good candidates.

According to the Unicode spec, the zero-width space "is not a visible separation, but it may expand in passages that are fully justified." However, it seems that the same is true of the ZWNJ as well (at least on the Kindle), which also shows up as a visible space between characters in justified text.

Is this another Kindle rendering bug, or is it normal behaviour? If it's normal behaviour, is there something else I could use that it guaranteed never to be expanded into a space in justified text (i.e. a "soft line break" character)?

[theducks]

This is not a Calibre question.
This in not a Calibre Editor question. The Editor is simply a tool to put a batch of characters into a valid e-book format.

It is a generic (uni)Coding question. (The question was not 'How do I insert" or 'The Editor does not show this correctly')

It will stay here for now. At least until someone else determines what Format/Writing forum it really belongs in.

I suspect from the wording, the closest MR fit is Kindle format.

Please don't blame the tools for device feature deficiencies.

[Phssthpok]

Yeah, I couldn't figure out where to ask this either. I thought this was a good place because lots of people ask things like "how do I centre a paragraph" and other HTML formatting stuff. I asked here because I am editing a book and trying to find the right way to achieve a particular formatting effect -- namely, a "soft line break" that will not be expanded into a visible space within a line of text.

[Phssthpok]

BTW: further testing seems to confirm that this is indeed a Kindle rendering bug. So I will continue to format things using &zwnj's and try to find a Kindle-specific forum where I might be able to get a sensible answer.