ptg1647605252 LESSON 3: Introducing HTML and CSS
A Short History of HTML Standards
HTML 2.0 was the original standard for HTML and the set of tags that all browsers
should support. Most of the tags in that original specification are still supported and still
make up the core of HTML. You can create perfectly good web pages using only tags
that were included in HTML 2.0.
The HTML 3.2 specification was developed in early 1996. Several software vendors,
including IBM, Microsoft, Netscape Communications Corporation, Novell, SoftQuad,
Spyglass, and Sun Microsystems, joined with the W3C to develop this specification.
Some of the primary additions to HTML 3.2 included features such as tables, applets, and
text flow around images.
HTML 4.0, first introduced in 1997, incorporated many new features that gave designers
greater control over page layout than HTML 2.0 and 3.2. Like HTML 2.0 and 3.2, the
W3C created the HTML 4.0 standard.
Frames (originally introduced in Netscape 2.0) and floating frames (originally introduced
in Internet Explorer 3.0) were introduced with the HTML 4.0 specification. Frames are
discussed in more detail in Lesson 20, “Working with Frames and Linked Windows.” By
far, however, the most important change in HTML 4.0 was its increased integration with
Cascading Style Sheets.XHTML
The specification that followed HTML 4.0 was XHTML 1.0, which was followed by
XHTML 1.1. The most significant new change introduced with XHTML was that it
required that HTML documents to also be valid Extensible Markup Language (XML)
documents. The X in XHTML stands for XML. XML is another markup standard derived
from SGML. XML is a language used to create other markup languages, and XHTML is
one such language. The main difference from HTML is that XHTML requires documents
to conform to XML’s strict rules for document structure. Whereas HTML 4 was forgiv-
ing of unclosed elements, XML requires that every tag be closed, every attribute have a
value, and more.
Technically, XHTML and HTML 4 were very similar. The actual tags and attributes are
almost the same, but the XML rules required large changes to many websites.
While XHTML has been superseded by HTML5, most websites that currently exist were
built using XHTML. If you’re working on a site that was built with XHTML, you must
adhere to a few rules if you want your HTML markup to be valid XHTML. All of these