Answer 1

When you look at SGML, HTML, and XML, you could consider this a family grouping. SMGL, HTML and XML are all markup languages. The term markup gets its root from editors making revisions to writer‚s manuscripts. An editor, when reviewing the content, will ’mark up‚ the manuscript to highlight certain fields. In computer technology, a markup language is a set of words and symbols that highlight text to define it for a web document.
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https://www.thoughtco.com/relationship-between-sgml-html-xml-3469454

Answer 2

They all have -ML in their names.