HTML Validation

HTML Validation is the process of validating HTML code against a standard. The W3C (World Wide Web Consortium, headed by Tim Berners Lee (HTML and HTTP's creator) supplies the DTDs and Schemas for the various versions and types of HTML. But, the W3C don't produce web browsers, or web servers, so each maker can interpret the DTDs in their own fashion, some extend and some ignore, very few are 100% compliant, some are more compliant than others though.

This variation makes validation a bit of a minefield, it is wise to create sites with the W3C recommendations but change these sites if the major browsers don't render or operate in the desired fashion. It may also make sense to develop sites at high speed, and if the render is fine not to worry about validation. The web is very much commercial nowadays, so people develop against time lines and speed to market for some can be crucial.

Validation has a number of pros or positive points to it, generally more tools will work with valid code than invalid code, the process of validation may uncover more fudnamental errors in the document itself, and valid documents tend to be better indexed by search engines.

HTML Document Type Definitions

Document Type Definitions

Validation Tools

Validation tools are useful to check that markup is valid against a particular standard. Care should be taken though as the validation tool may be incorrect in their validation result.