Forms have been a mainstay of web pages, providing the means to communicate with the server and receive a response, for almost as long as there has been a World Wide Web. However, not much has changed between those original form elements and the XHTML form elements of today. Sure, there are differences, especially when forms were made to conform to XML conscripts. But how the form elements work and interact with the user is still the same.
What has changed, thanks in large part to Ajax technologies, is how the form is used for communication with the server. With Ajax, the client no longer has to refresh the entire page with each form submission. Instead, communication with the server can occur without a refresh, and only the parts of the page requiring an update or refresh get one. As you will see, this only touches on the overall effect Ajax has had on forms. As I go into more detail, you will see the true power of forms in modern web applications.
As I said in the introduction to the chapter, forms did not change much as they moved to XHTML and the world of XML. However, it is important to know the changes and idiosyncrasies of XHTML forms in order to build an accessible and standards-compliant form in an Ajax application.