All HTML and XHTML pages should use the element to define which HTML version to follow. The doctype defines the HTML version you are using and gives the browser important information to render your page more quickly and consistently.
Verifier is a software program that checks to see if a web page is standard. When using validators to inspect HTML, XHTML, or CSS files, the validator returns a list of errors based on your chosen criteria.
Web standards make web development easier. Web standards are set by the World Wide Web Consortium (W3C). It is even better for web developers and web developers to adhere to the specified standards when developing new applications for better web development.