What I find astonishing is that Apple's spellchecking does such a shocking job of fixing the huge numbers of errors its own autofill creates.
The procedure is:
1. Drops the initial letters as you type because it can't seem to keep up
2. Sticks on the Caps key so you get two Caps at the beginnings of words.
3. Badly anticipates or guesses your typing and word substitutes when you are not looking
4. Causes yet more delays in the typing as the slow spellchecking spellchecking kicks in
5. Mostly gets it wrong due to the fight between you and the keyboard
6. Inputs egregious errors where there should have been none, actually substitutes nonsense for good typing
7. Again fights your attempts to manually correct the MacOSX errors
8. Does it all with time delays
In summary, like most of Apple's software in the last 3-4 years, it takes perfectly good solutions and makes you look like an idiot when you hit send without triple checking.
Look forward to Apple introducing Autocorrection to its Autocorrection. Expect it to work about as well at Autocorrecting itself as it Autocorrects you.
Peter
Had virtually all these issues just typing this post. Hope I didn't miss anything manually correcting the mess. The latest thing in MacOS Sierra is involuntary zooming into the screen. So yet another thing to constantly interfere in and slow down my work.
...and being Apple, MacOS and iOS have different implementations of the selection of suggested words!!!