XML is a subset of SGML. A valid XML document is also a valid SGML document, but the vice versa isn't true.
Does this keep true even if I use the XML Schema instead of the DTD?
The doubt stems from that fact that the XML DTD is a subset of the SGML DTD, but the XML Schema allows things that can't be defined in the XML DTD.
So is XML Schema still a subset? Can I do with SGML DTD everything I can do with XML Schema?