Ah yes, I definitely intended a hat tip to Engelbart but I forgot to include it in the article. I reinvented it only semi-independently.
Great write up. Question: why does the one keycap on the 'behold' photo look like it is so much less high? (on the other photo they seem identical)
One of the keycaps is from a different row, so it has a different height on one side, but on the other side they're the same height.