HyTime (Hypermedia/Time-based Structuring Language) is a markup language that is an application of SGML.
HyTime defines a set of hypertext-oriented element types that, in effect, supplement SGML and allow SGML document authors to build hypertext and multimedia presentations in a standardized way.
HyTime is an international standard published by the ISO and IEC.
[3] Some of the concepts formalized in HyTime were later incorporated into HTML and XML: The HyTime standard itself is ISO/IEC 10744, first published in 1992 and available from the International Organization for Standardization.
It was developed by ISO/IEC JTC 1/SC 34 (ISO/IEC Joint Technical Committee 1, Subcommittee 34 - Document description and processing languages).