Learning HTML 3.2 by Examples, section 1 Preface:

But why HTML 3.2?

The HTML language exists in several variants and continues to evolve, but the HTML 3.2 constructs will most probably be usable in the future, too. By learning HTML 3.2 and by sticking to it as far as possible, you can produce documents which can be browsed by a large variety of Web software now and in the future. Later you may learn to add some useful constructs defined in HTML 4.0 (or future HTML standards as they are defined). This does not exclude the possibility of using other features, such as enhancements provided by Netscape Navigator or Internet Explorer or some other product, if it really serves your purposes and you are willing to accept the consequences (e.g. limitations on accessibility). But it is wise to adopt the habit of producing documents in a standardized language and using extensions only when really necessary.

HTML 3.2 has been defined by the World Wide Web Consortium, W3C. It is supported by several browsers to a large extent, and it will probably become the common basis understood by almost all relevant Web software.

The next version of HTML, an extension to HTML 3.2, is known as HTML 4.0 (or the code name Cougar). It was approved as a W3C recommendation in December 18th, 1997, but it takes time before there will be new browser versions which support it and before users widely upgrade to such versions. In particular, Netscape 4.0 and Internet Explorer 4.0 do not support HTML 4.0 in general; see especially Stephanos Piperoglou's HTML 4.0 in Netscape and Explorer (to which I have some minor annotations). Thus, for quite a long time, netwise long, it will be safest to use HTML 3.2, adding useful HTML 4.0 features when needed. If possible, when using HTML 4.0 try to do things so that they "degrade gracefully" on browsers which only support HTML 3.2. On the other hand, the HTML 4.0 specification makes some HTML 3.2 elements and attributes "deprecated", but they are mostly for presentational features and not recommended in this document anyway; and in this document the note "Deprecated in HTML 4.0" is given for them. Moreover, there are changes to the syntax of some elements which impose stricter rules than HTML 3.2. Some of these stricter rules apply to "HTML 4.0 Strict" only; the HTML 4.0 specification defines the Strict (and recommended) syntax as well as the more permissive Transitional syntax, recommending that new documents use Strict. Therefore, and since such strictness requires just a little attention from the author, appropriate notes about the stricter syntax rules in HTML 4.0 are given in the presentation of elements in this document.

An older standard, HTML 2.0, is supported to an even larger extent, since HTML 3.2 is an extension of HTML 2.0.

However, to be exact, the following HTML 2.0 features have been removed in HTML 3.2:

It might be a good idea to try to write your documents in HTML 2.0 if possible (avoiding the above-mentioned omitted features, of course). For this reason, constructs (e.g. tags, tag attributes, or attribute values) which are legal HTML 3.2 but not HTML 2.0 are flagged in this document as follows: (Not in HTML 2.0!) Notice that even by sticking strictly to HTML 2.0 you cannot absolutely guarantee a proper rendering of your documents, since there are deficiencies in browser implementations.
Date of last update: 2010-12-16.
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