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🤔 If by "substitute for HTML", you mean something like "for creating websites", I guess the answer is no, not really. I think that since HTML is a "living standard" it supposedly evolves toward improvement. There are definitely markup languages that are better for other use cases. https://en.m.wikipedia.org/wiki/List_of_document_markup_languages
In past, facebook introduced fbml, specifically for embedded fb action buttons etc. Initially for mobile devices wml had been used in making wapsites. I know HTML is currently the most important part of websites but, Technological improvements are always there, so i just asked in that sense. Anyway thanks 😊💐
All other code would also be depreciated in the process. It's required for the world wide web.