[quote=“Buddy, post:31, topic:820”]
The reason that double tilde strikethrough should be in the standard is because it already is standard, and the point of having a standard is to specify the standards that are standard.[/quote]
@codinghorror and @jgm have already stated that the intent of this particular standard is to give a specification of core Markdown elements. Not all standards need to codify every element in wide use. In this case, that’s what the extensions will be for.
In practical terms (for writers), is there a difference whether a feature in part of the core or an extension? App developers will either implement support for an element or they won’t. This is independent from whether the element is part of the core or if it is part of an extension. So long as the element is included (one way or another) in CommonMark is there a problem?