Talk:IBM Generalized Markup Language

HTML and XML aren't really applications of SGML. HTML started life as it's own format which happened to use pointy brackets. SGML was retrofitted to HTML - later standardised versions had an SGML DTD associated to them. However I suspect a minute percentage of HTML pages at any point in time were ever valid and compatible with an SGML parser.

Saying XML is an application of SGML is completely wrong. XML has its roots in SGML, but it is not an application of it.

SGML is a system for creating application specific data formats - each of these uses is an 'application'. Ditto XML is a system for creating application specific data formats, and has it's applications.

XML was created to be "SGML for the web". It introduced backward incompatible changes - DTDs were optional, introduced the empty tag syntax, it supported Unicode etc. At the point of its creation, XML was not a subset of SGML - some well formed or even valid XML files were not compatible with SGML. This is not a flaw, XML set out to be a different standard.

Later on, the SGML standard was extended so that XML files could be considered a subset of SGML documents, but that is a recent development in the history of SGML.