Day3

 was published as a recommendation by the World Wide Web Consortium . It provides three forms:

Strict, as neglected items are prohibited.

Transitional, where neglected elements are allowed

Frame set, in which mostly only frame related items are allowed .

Initially codenamed "Cougar",  HTML 4.0 adopted many browser-specific element types and attributes, but at the same time sought to phase out Netscape's visual markup features by marking them as obsolete in favor of style sheets. HTML 4 is an implementation of SGML that conforms to ISO 8879 - SGML. 

April 24, 1998

 was re-released with minor modifications without increasing the version number.

December 24, 1999

HTML 4.01  was published as a W3C Recommendation. It provides the same three forms as HTML 4.0 and its last bug was published on May 12, 2001.

May 2000

 (" ISO HTML", based on HTML 4.01 Strict) was published as an ISO/IEC international standard. In ISO, this standard falls within the scope of ISO/IEC JTC1/SC34 (Joint Technical Committee 1 ISO/IEC, Subcommittee 34 - Document description and processing languages). 

After HTML 4.01, there was no new version of HTML for many years because the development of the parallel XML-based XHTML language occupied the HTML Working Group at the W3C during the early and mid-2000s