From ISO/IEC 10744:1992.
© International Organization for Standardization 1992. Permission to copy in any form is granted for use with conforming HyTime systems and applications as defined in ISO/IEC 10744, provided this notice is included in all copies.
Explicit hypertext implied from the Standard added by Chris Maden.
[This document was created in 1997 as I was learning HyTime; I got distracted with actual work before finishing it, but I've kept it for historical interest. I've deliberately decided not to update it from its original HTML 2.0 for that reason.]