only sort of.
this is the original document defining markdown, and you’ll notice it doesn’t really specify a lot of the things that have compatibility issues across different markdown processors, along with allowing arbitrary html which really depends on where you’re showing it. There’s a list of ambiguous syntax here.
CommonMark is as close to a standard as we have.
for people ootl on D like me, this seems to explain the problems: https://dpldocs.info/this-week-in-arsd/Blog.Posted_2024_01_01.html