Both XML and HTML are implementations of SGML. SGML is the parent reference and includes things that aren't in either subset. SGML was invented by IBM for "pub

Both XML and HTML are implementations of SGML. SGML is the parent reference and includes things that aren't in either subset. SGML was invented by IBM for "pubs," authoring documents electronically but shipping them as printed manuals. Lacking the need for print (in HTML) and for display (in XML) lead to those versions.