The older ones among us remember when XML took over the world and everyone was supposed to use strict XHTML. It turned out that the strength of the HTML ecosystem was its fault tolerance. HTML4 was the "sloppy" answer to XHTML. It brought HTML back from a data language to a markup language. Every Markdown parser is similarly fault-tolerant as HTML parsers.
However, CSS and JS are not error-tolerant. A syntax error in a CSS rule causes it to be ignored. An unhandled JavaScript exception is a hard stop. This way, web does not run on tolerance.
However, CSS and JS are not error-tolerant. A syntax error in a CSS rule causes it to be ignored. An unhandled JavaScript exception is a hard stop. This way, web does not run on tolerance.