9.1 Form Fundamentals

Forms are comprised of one or more text-input boxes, clickable buttons, multiple-choice checkboxes, and even pull-down menus and image maps, all placed inside the <form> tag. You can have more than one form in a document, and within each you may also put regular body content, including text and images. The text is particularly useful for providing form element labels and prompts and instructions to the users on how to fill out the form. And, within the various form elements, you can use JavaScript event handlers for a variety of effects, such as testing and verifying form contents and calculating a running sum.

A user fills out the various fields in the form, then clicks a special "Submit" button (or, sometimes, presses the Enter key) to submit the form to a server. The browser packages up the user-supplied values and choices and sends them to a server or to an email address.^[1] The server passes the information along to a supporting program or application that processes the information and creates a reply, usually in HTML. The reply may simply be a thank you, or it might prompt the user on how to fill out the form correctly or to supply missing fields. The server sends the reply to the browser client, which then presents it to the user. With emailed forms, the information is simply put into someone's mailbox; there is no notification of the form being sent.

^[1] Some browsers, Netscape and Internet Explorer in particular, may also encrypt the information, securing it from credit-card thieves, for example. However, the encryption facility must be supported on the server as well: consult the web server documentation for details.

The server-side, data-processing aspects of forms are not part of the HTML or XHTML standards; they are defined by the server's software. While a complete discussion of server-side forms programming is beyond the scope of this book, we'd be remiss if we did not include at least a simple example to get you started. To that purpose, we've included at the end of this chapter a few skeletal programs that illustrate some of the common styles of server-side forms programming.