HTML and CSS Reference
In-Depth Information
9.1. Form Fundamentals
Forms are composed 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 one you also may put regular body con-
tent, including text and images. The text is particularly useful for provid-
ing form element labels, 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. [*] The server passes
the information along to a supporting program or application that pro-
cesses the information and creates a reply, usually in HTML. The reply
simply may 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.
[*] The popular browsers may also encrypt the information, securing it from credit card thieves, for ex-
ample. 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 standard; they are defined by the server's software.
While a complete discussion of server-side forms programming is beyond
the scope of this topic, 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.
A final caveat: as is its wont, the World Wide Web Consortium (W3C)
has been working on an XML-based definition of forms. This new version
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