Freelance web developers
A web developer is the person who deals with the code that drives websites that makes the functionality of them work. For example PHP, XHTML and CSS, ASP. Dot Net and Ruby on rails.
Most follow web standards which utilises valid XHTML and CSS to control the layout and design. This also naturally helps with search engine optimization.
Web developers are very clever people usually with a degree in math, IT or Computer Science as this is what makes websites function. At the end of the day, everything you see and do on the internet is programmed so it can presented to you in the browser in a usable and understandable manner!