good points!

to add:

There will always be extensions that particular applications support and others do not. Some writers use footnotes, mathematical notation, diagrams, embedded HTML or specialized publishing syntax that goes beyond CommonMark and GitHub Flavored Markdown. I do not expect every built-in document viewer to reproduce every possible extension exactly.

the author initially wants full hardware support of markdown, but then backpedals to only the specs, i assume, he likes.