Some websites are entirely static. They are the same every time you visit. You never give them information; there are no polls, bulletin boards, or referral forms. If you want to find something on the website, there is no search box, you just look around until you find it. But such sites are growing more rare as the internet becomes an ever greater part of people’s lives.

Modern sites are searchable. They offer new images on each visit. They allow the user to request more information or to post their own thoughts. Many can be updated directly from a simple panel or word-processing program. A lot of websites are data-driven, meaning that web pages are actually created on the fly, in response to the specific needs of the user. All of these functional elements are called backend elements. In some cases there are many different ways to do the same thing, so the line between elements is often blurry.