Aren't HTML, SGML, and XML all very similar things

Question

Aren't HTML, SGML, and XML all very similar things?

Answer 1

Not fairly; SGML is the mother tongue, and has been used for explaining thousands of various document types in many fields of human activity, by transcriptions of ancient Irish manuscripts for stealth bombers to the technical documentation, and by patients' clinical records to musical notation. It is very large and complicated, however, and possibly overkill for most common office desktop applications.

XML is an abbreviated version of SGML, to make this easier to use over the Web, easier for you to describe your own document types, and simple for programmers to write programs to handle them. This omits all the complex and less-used options of SGML in return for the advantages of being easier to write applications for, simpler to understand, and more suited to delivery and interoperability over the Web. But this is yet SGML and XML files may even be processed in similar way as any other SGML.

HTML is only one of many SGML or XML applications. The one most often used on the Web. Technical readers may get it more useful to think of XML as being SGML-- quite than HTML++.