Sitecore is a rich platform with powerful web content management capabilities.One of the standard available features are validators that automatically execute as a part of the publishing workflow.In short, the validator will let you know if your markup conflicts with the specification, so it’s still a valuable tool when developing your pages.
This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, Math ML, etc.
If you wish to validate specific content such as RSS/Atom feeds or CSS stylesheets, Mobile OK content, or to find broken links, there are other validators and tools available.
Indeed, most developers creating rich Web applications know that reliable scripting needs the document to be parsed by User-Agents without any unexpected error, and will make sure that their markup and CSS is validated before creating a rich interactive layer.
Checking that a page "displays fine" in several contemporary browsers may be a reasonable insurance that the page will "work" today, but it does not guarantee that it will work tomorrow.
Validating a HTML document means checking or verifing its code according to the standards of HTML5 specifications.
For validating an HTML5 document we can use an HTML validator.Beginners and students, on the other hands, will find automated checking tools invaluable in spotting mistakes.Some teachers also stress that automated validation tests are a good introduction to broader, more complex quality concepts such as accessibility.In the past, many authors who relied on the quirks of Netscape 1.1 suddenly found their pages appeared totally blank in Netscape 2.0.Whilst Internet Explorer initially set out to be bug-compatible with Netscape, it too has moved towards standards compliance in later releases.So, you ask, what count as an error for the HTML5 validator?