Why would I want to put information on my web page that is not visible to the typical viewer?

Someone might want to put information that is not visible in order to make viewing more convenient. Having things that are invisible to the viewer such as DOCTYPE are important to displaying the page. There are also tags, called metadata, that are invisible but have many purposes. They can change how the page looks by using the title,style,charset, and viewport tags. Metadata is very useful for viewers making it easier.