11 HTML Validation
Validation of a web page checks the content and structure of the web page follows the standard rules defined by different organizations, mainly W3C.
W3C offers a freely available tool Markup Validation Service.
This validator checks the markup validity of web documents in HTML, XHTML, SMIL, MathML, etc.
Validation is very important, because it assures web pages will be correctly displayed by different software (mainly, browsers). When a page has some HTML errors, different browsers will show different results because browsers' behaviour is not defined in the oficial recommendation.
Some common HTML mistakes that affect accessibility of web content are (extracted from 12 Common HTML Mistakes):
- Missing or incorrect DOCTYPE.
- Missing character encoding.
- Unsupported tags or attributes.
- Improperly formatted HTML.
- Improper tables.
- Improper use of form tags.