Standard Generalized Markup Language is the full from of SGML.
View page
HTML is a subset of SGML (Standard General Markup Language) with
more forgiving rules that are not followed for XHTML and XML (also
subsets.)
View page
Standard Generalized Markup Language marked the beginning of
style sheets in 1980s.
View page
HyperText Markup Language. It's a derivative of GML, Generalized
Markup Language, which was used for producing complicated documents
on a computer in the days before WYSIWYG editors were common.
View page
It is programming languages that are referred to in terms of "high level" and "low level".
Extensible Markup Language(XML) is a markup language not a programming language, it is a data formatting specification that makes the presentation of data independent of programs (so that data can be passed between programs).
For this reason the answer to your question is "neither".