These were formallly specified in the Jun 15 1995 HTML
2.0 draft specifications. I have a local copy of this
archive, and the associated
documentation, on my server at: HTML2-15Jun95/.
HTML 3 was the last IETF "draft" specification for HTML: this
never became a formal standard. I haven't been able to locate
a copy of the final version of this draft ... if anyone knows
where it is, please let me know.
Similarly, I know of no definitive references for the DTDs,
entity definition files, etc., although the ones that I use
were originally obtained from the draft standard.
This was the first version of HTML released as a
World Wide Web Consortium recommendation. The draft
draft specification is found at at:
http://www.w3.org/MarkUp/Wilbur/.
The DTD, entity declaration and catalog files are
all available from the preceding document.
The HTML 4.0 specification documents are no longer available,
as they were superceded by HTML 4.01. Various earlier working
drafts can be found at:
http://www.w3.org/TR/WD-html40-970917/.
Each specification document references the DTDs, entity and
other files, and also references previous drafts.
HTML 4.01 is defined in the official HTML 4.01 specification,
found at: http://www.w3.org/TR/REC-html40/.
This is a simple update to HTML 4.0 that fixed some small errors.
The DTDs, entity definition files, an so on, are found via the file: http://www.w3.org/TR/REC-html40/sgml/intro.html.
This was and is the last version of HTML. The language has now been
superseded by XHTML.