Preserving skills: Refining declarative markup for future generations

The document world is experiencing an ice age, a descent into tribalism and chaos, as the ideas behind declarative markup are forgotten and a leap has been made from What You See Is All You Get word processors and (worse) page layout software into the now-ubiquitous README.md markdown format, in which what you see is less than what you get and not at all what you need.

In twenty years, in ten years, next week some time, will the ideas behind declarative markup be forgotten? If so, who will keep the iron wheels turning in the mineshafts of technology?

What must we record, write down, vlog, so that people who come after us can keep the system working, let alone make new systems?