Open the test.cpp attachment in Qt Creator and attempt to rewrap the paragraphs. The first two contain no-break spaces and Qt Creator should not break at them, but does. Attempting the same wrapping in Emacs (c-fill-paragraph) properly breaks at the real spaces before "tone".

Emacs does not break at the zero-width examples below and neither does Qt Creator.

Use-case: write things like "4 kB" such that the 4 and the k aren't separated into multiple lines.