Marking up and marking down

Markup provides a means of annotating a text such that its important characteristics are readily apparent. Simplicity of annotation and richness of meaning are often at odds. Through one lens, we can see the evolution of markup as developing along this fault line. TANSTAAFL. SGML provided mechanisms that reduced the complexity of annotation at considerable cost in implementation. XML reduced implementation cost at the expense of simplicity in annotation. HTML attempted to simplify annotation complexity and implementation cost by choosing a single tag set and inventing entirely new extension mechanisms. Online communities like GitHub and Stack Overflow have abandoned angle brackets in favor of Markdown, Common Mark, AsciiDoc, and other markup reminiscent of wiki syntax or SGML SHORTREF. Why am I in this basket and where are we going?