Well that was weird. I am used to Microsoft Word automatically spell checking as I go. And then I realised it had stopped doing it. Then I realised it was doing it in bits of my document, and not others. So I copied and pasted and experimented and cursed. Then I switched on the option that shows all the hidden codes and it all looked ok. I couldn’t see why it was ignoring just sections of the document. e.g.

What I didn’t realise is that Word appears to allow you to switch off spell-checking on certain parts of your document. But it isn’t obvious which bits. I found that when I dropped the mouse about in the unchecked bit then selected: Review / Language / Set Proofing Language
it was configured to ignore that section. Or Word. Letter. Character. Dunno how or why it decided to ignore that bit. I don’t know where the not-checking section begins and ends, or how to find out. i.e.

So I unchecked Do not check spelling and grammar
and everything is hunky dory. Mystery solved.
Well, not really. Why did that option get checked in the first place? I didn’t do it.
I have a theory that it’s something to do with something that happened a couple of days ago. Out of the blue Word popped up with a glittering selection of all my spelling mistakes and dictionary additions for the past few months, and asked me if I would mind awfully if it sent them anonymously to Microsoft. I said I did mind, politely declined the request, and asked not to be asked again. Perhaps it was something to do with that. Perhaps Bill is cross with me.