OK.
It does have a real time spell checker. But it doesn't seem to have the squiggly line. The screen blinks at you when you type a word it can't find.
I've just run Prowrite 2 and 3.1.1 via FS-UAE.
So my memory is wrong about that feature have a red squiggly line.
It did have realtime checking. Also Prowrite was WYSIWYG. The realtime checking is neat, but it's actually a bit annoying with the blink. The red squiggly line is a better way to show that there is an unrecognised word.
Thanks for getting me to check.