The World Wide Web is a network of information resources. The Web relies on three mechanisms to make these resources readily available to the widest possible audience:
The ties between the three mechanisms are apparent throughout this specification.
Every resource available on the Web -- HTML document, image, video clip, program, etc. -- has an address that may be encoded by a Uniform Resource Locator, or "URL".
URLs typically consist of three pieces:
Consider the URL that designates the current HTML specification:
This URL may be read as follows: There is a document available via the HTTP protocol (see [RFC2068]), residing on the machine www.w3.org, accessible via the path "/TR/PR-html4/cover.html". Other schemes you may see in HTML documents include "mailto" for email and "ftp" for FTP.
To publish information for global distribution, one needs a universally understood language, a kind of publishing mother tongue that all computers may potentially understand. The publishing language used by the World Wide Web is HTML (from HyperText Markup Language).
HTML gives authors the means to:
HTML was originally developed by Tim Berners-Lee while at CERN, and popularized by the Mosaic browser developed at NCSA. During the course of the 1990s it has blossomed with the explosive growth of the Web. During this time, HTML has been extended in a number of ways. The Web depends on Web page authors and vendors sharing the same conventions for HTML. This has motivated joint work on specifications for HTML.
HTML 2.0 (November 1995, see [RFC1866]) was developed under the aegis of the Internet Engineering Task Force (IETF) to codify common practice in late 1994. HTML+ (1993) and [HTML30] (1995) proposed much richer versions of HTML. Despite never receiving consensus in standards discussions, these drafts led to the adoption of a range new features. The efforts of the World Wide Web Consortium's HTML working group to codify common practice in 1996 resulted in HTML 3.2 (January 1997, see [HTML32]). Changes from HTML 3.2 are summarized in Appendix A
Most people agree that HTML documents should work well across different browsers and platforms. Achieving interoperability lowers costs to content providers since they must develop only one version of a document. If the effort is not made, there is much greater risk that the Web will devolve into a proprietary world of incompatible formats, ultimately reducing the Web's commercial potential for all participants.
Each version of HTML has attempted to reflect greater consensus among industry players so that the investment made by content providers will not be wasted and that their documents will not become unreadable in a short period of time.
HTML has been developed with the vision that all manner of devices should be able to use information on the Web: PCs with graphics displays of varying resolution and color depths, cellular telephones, hand held devices, devices for speech for output and input, computers with high or low bandwidth, and so on.
HTML 4.0 extends HTML with mechanisms for style sheets, scripting, frames, embedding objects, improved support for right to left and mixed direction text, richer tables, and enhancements to forms, offering improved accessibility for people with disabilities.