One of the first things that should be done after a site is constructed, and repeated at various steps as things are changed/updated, is the validation of the site's HTML.
In the case of a Joomla powered site, HTML errors can come from 4 places: It's simple really; HTML errors can present unwanted issues with your site, and is the leading cause of issues with template display that we see.
Validation is important, and will ensure that your web pages are interpreted in the same way (the way you want it) by various machines, such as search engines, as well as users and visitors to your webpage.
Instead, with HTML5 web pages served over HTTP, the validator follows browser behaviour and determines the HTML serialization using the content-type setting. uri= automatically)&doctype=Inline&ss=1&group=0&user-agent=W3C_Validator/1.2 Notice that in a browser both here: xml/ashx and validated here: Similarly, if you create a new document (that you have not yet saved), you can set its grammar, but only to HTML, not specifically to XHTML. Here's my problem: those new documents have no file extension.(I could just open the sample documents, but I'd prefer not to do that, to avoid the user inadvertently updating them.Make sure your codes and styles validate across the board.That means they have to meet the "strict" standards set by the W3C Organization and pass a variety of validations for CSS and XHTML. Some only check CSS, others XHTML, and others for accessibility.Input your page address in the box below − This validator checks the markup validity of web documents with various formats especially in HTML, XHTML, SMIL, Math ML, etc.