Start of a design for a screen/block editor from scratch using basic built-in words only.
Full PlasMa playlist:
https://youtube.com/playlist?list=PLI2uGjCObnyTZ5FLeW3wmIPQseOdsQ1p6
More details, including the Build Guide document and other downloads for the PlasMaSim simulator and Plasm assembler, at http://www.philizound.co.uk/plasma/plasma.html