How do I toggle the Outliner view (to the right of the (N) viewport (3D) properties region?)
e.g. to get more Viewport space for some reason or another?
You can try Alt F10 with the curser in the viewport you want to expand to full screen. Alt F10 brings it back. You can also grab the edge with the curser and drag it over.
I didn't mean Full Screen, naturally I revert to that for max space, but I meant temporarily hiding the region, i.e. the same as pressing "N" for the Viewport Props (inner right) or "T" for the Toolbar (Leftmost).. Similar, but show/hide the outer? Sorry, I probably didn't explain clearly enough (still new so my explanations are somewhat thwarted!)