(The <200b> is also highlighted a different color than the rest of the text, and acts like a single character when moving the cursor through it. It's really, really obvious.)
In emacs those characters are by default visible as one-pixel wide spaces, to make them more apparent eval (update-glyphless-char-display 'glyphless-char-display-control '((format-control . empty-box) (no-font . hex-code))).