If I see a gap between two lines of text, and that gap vanishes when I commit the document to the web or save it to a file, then it’s not ‘WYSIWYG’. But this has been my experience with 100% of such editors.
I propose a new acronym to replace ‘wizzy-wig’:
WYSMBWYGIYLBIACWBFRTWNBMCTYSSIYUC
What You See Might Be What You Get if You’re Lucky but it Almost Certainly Won’t Be For Reasons That Will Never Be Made Clear to You So Suck it Ya Ugly Cunt
Not as pithy, but at least it’s accurate.
Try VisualEditor on e.g. Wikipedia. You notice idiosynchrasies if you’re doing something specific or are pretty experienced, but overall, the difference between the editor and the preview (fully rendered page) is trivial unless you’re messing around with a few specific elements (even then, a quick ‘Preview’ fills in this gap).