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HTML versions

July, 1993: Hypertext Markup Language, was published at IETF working draft (that is, not yet a standard).

November, 1995: HTML 2.0 published as IETF Request for Comments:

• RFC 1866,
• supplemented by RFC 1867 (form-based file upload) that same month,
• RFC 1942 (tables) in May 1996 ,
• RFC 1980 (client-side image maps) in August 1996 , and
• RFC 2070 (internationalization) in January 1997 ;

Ultimately, all were declared obsolete/historic by RFC 2854 in June 2000 .

An HTML 3.0 standard was proposed to the IETF by Dave Raggett and the newly formed W3C in April 1995. It proposed many of the capabilities that were in Raggett's HTML+ proposal, such as support for tables, text flow around figures, and the display of complex mathematical elements. Even though it was designed to be compatible with HTML 2.0, it was too complex at the time to be implemented. Browser vendors opted to support only parts of the proposal, but implemented other markup constructs that they wanted to be incorporated into the standard. When the draft expired in September 1995, work in this direction was discontinued due to lack of browser support. HTML 3.1 was never officially proposed, and the next standard proposal was HTML 3.2 (code-named "Wilbur"), which dropped the majority of the new features in HTML 3.0 and instead adopted many browser-specific element types and attributes that had been created for the Netscape and Mosaic Web browsers.

January 14, 1997: HTML 3.2, published as a W3C Recommendation.

HTML 3.2 was never submitted to the IETF, whose HTML Working Group closed in September 1996; it was instead published as one of the W3C's first "Recommendations" in early 1997. Mathematical support as proposed by HTML 3.0 finally came about years later with a different standard, MathML.

December 18, 1997: HTML 4.0, published as a W3C Recommendation. It offers three "flavors":

• Strict, in which deprecated elements are forbidden,
• Transitional, in which deprecated elements are allowed,
• Frameset, in which mostly only frame related elements are allowed;

HTML 4.0 (initially code-named "Cougar") likewise adopted many browser-specific element types and attributes, but at the same time began to try to "clean up" the standard by marking some of them as deprecated, and suggesting they not be used. Minor editorial revisions to the HTML 4.0 specification were published in 1998 without incrementing the version number and further minor revisions as HTML 4.01.

April 24, 1998: HTML 4.0 was reissued with minor edits without incrementing the version number.

December 24, 1999: HTML 4.01, published as a W3C Recommendation. It offers the same three flavors as HTML 4.0, and its last errata were published May 12, 2001.

HTML 4.01 and ISO/IEC 15445:2000 are the most recent and final versions of HTML.

May 15, 2000: ISO/IEC 15445:2000 ("ISO HTML", based on HTML 4.01 Strict), published as an ISO/IEC international standard.

January 22, 2008: HTML 5, published as a Working Draft by W3C.

XHTML versions

XHTML is a separate language that began as a reformulation of HTML 4.01 using XML 1.0. It continues to be developed:

• XHTML 1.0, published January 26, 2000 as a W3C Recommendation, later revised and republished August 1, 2002. It offers the same three flavors as HTML 4.0 and 4.01, reformulated in XML, with minor restrictions.
• XHTML 1.1, published May 31, 2001 as a W3C Recommendation. It is based on XHTML 1.0 Strict, but includes minor changes, can be customized, and is reformulated using modules from Modularization of XHTML, which was published April 10, 2001 as a W3C Recommendation.
• XHTML 2.0 is still a W3C Working Draft. XHTML 2.0 is incompatible with XHTML 1.x and, therefore, would be more accurate to characterize as an XHTML-inspired new language than an update to XHTML 1.x.
• XHTML 5, which is an update to XHTML 1.x, is being defined alongside HTML 5 in the HTML 5 draft.

HTML markup

HTML markup consists of several key components, including elements (and their attributes ), character-based data types , and character references and entity references . Another important component is the document type declaration .

Elements

Elements are the basic structure for HTML markup. Elements have two basic properties: attributes and content. Each attribute and each element's content has certain restrictions that must be followed for an HTML document to be considered valid. An element usually has a start tag (e.g. <element-name> ) and an end tag (e.g. </element-name> ). The element's attributes are contained in the start tag and content is located between the tags (e.g. <element-name attribute="value">Content</element-name> ). Some elements, such as <br> , do not have any content and must not have a closing tag. Listed below are several types of markup elements used in HTML.

Structural markup describes the purpose of text. For example, <h2>Golf</h2> establishes "Golf" as a second-level heading, which would be rendered in a browser in a manner similar to the "HTML markup" title at the start of this section. Structural markup does not denote any specific rendering, but most Web browsers have standardized on how elements should be formatted. Text may be further styled with Cascading Style Sheets (CSS).

Presentational markup describes the appearance of the text, regardless of its function. For example <b>boldface</b> indicates that visual output devices should render "boldface" in bold text, but gives no indication what devices which are unable to do this (such as aural devices that read the text aloud) should do. In the case of both <b>bold</b> and <i>italic</i> , there are elements which usually have an equivalent visual rendering but are more semantic in nature, namely <strong>strong emphasis</strong> and <em>emphasis</em> respectively. It is easier to see how an aural user agent should interpret the latter two elements. However, they are not equivalent to their presentational counterparts: it would be undesirable for a screen-reader to emphasize the name of a book, for instance, but on a screen such a name would be italicized. Most presentational markup elements have become deprecated under the HTML 4.0 specification, in favor of CSS based style design.

Hypertext markup links parts of the document to other documents. HTML up through version XHTML 1.1 requires the use of an anchor element to create a hyperlink in the flow of text: <a>Wikipedia</a> . However, the href attribute must also be set to a valid URL so for example the HTML code, <a href="http://en.wikipedia.org/">Wikipedia</a> , will render the word " Wikipedia " as a hyperlink.To link on an image, the anchor tag use the following syntax: <a href="url"><img src="image.gif"></a>

Attributes

Most of the attributes of an element are name-value pairs, separated by "=", and written within the start tag of an element, after the element's name. The value may be enclosed in single or double quotes, although values consisting of certain characters can be left unquoted in HTML (but not XHTML). Leaving attribute values unquoted is considered unsafe. In contrast with name-value pair attributes, there are some attributes that affect the element simply by their presence in the start tag of the element (like the ismap attribute for the img element).

Most elements can take any of several common attributes:

• The id attribute provides a document-wide unique identifier for an element. This can be used by stylesheets to provide presentational properties, by browsers to focus attention on the specific element, or by scripts to alter the contents or presentation of an element.

• The class attribute provides a way of classifying similar elements for presentation purposes. For example, an HTML document might use the designation to indicate that all elements with this class value are subordinate to the main text of the document. Such elements might be gathered together and presented as footnotes on a page instead of appearing in the place where they occur in the HTML source.

• An author may use the style non-attributal codes presentational properties to a particular element. It is considered better practice to use an element’s son- id page and select the element with a stylesheet, though sometimes this can be too cumbersome for a simple ad hoc application of styled properties.

• The title attribute is used to attach subtextual explanation to an element. In most browsers this attribute is displayed as what is often referred to as a tooltip.

The generic inline element span can be used to demonstrate these various attributes:

This example displays as HTML ; in most browsers, pointing the cursor at the abbreviation should display the title text "Hypertext Markup Language.

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