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: http://xray.sai.msu.ru/~ustiansk/web/interact/forms.html
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Contents
An HTML form is a section of a document containing normal content, markup, special elements called controls (checkboxes, radio buttons, menus, etc.), and labels on those controls. Users generally "complete" a form by modifying its controls (entering text selecting menu items, etc.), before submitting the form to an agent for processing (e.g., to a Web server, to a mail server, etc.)
Here's a simple form that includes labels, radio buttons, and push buttons (reset the form or submit it):
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
<LABEL for="firstname">First name: </LABEL>
<INPUT type="text" id="firstname"><BR>
<LABEL for="lastname">Last name: </LABEL>
<INPUT type="text" id="lastname"><BR>
<LABEL for="email">email: </LABEL>
<INPUT type="text" id="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
Note. This specification includes more detailed information about forms in the subsections on form display issues.
Users interact with forms through named controls.
A control's "control name" is given by its name attribute. The scope of the name attribute for a control within a FORM element is the FORM element.
Each control has both an initial value and a current value, both of which are character strings. Please consult the definition of each control for information about initial values and possible constraints on values imposed by the control. In general, a control's "initial value" may be specified with the control element's value attribute. However, the initial value of a TEXTAREA element is given by its contents, and the initial value of an OBJECT element in a form is determined by the object implementation (i.e., it lies outside the scope of this specification).
The control's "current value" is first set to the initial value. Thereafter, the control's current value may be modified through user interaction and scripts.
A control's initial value does not change. Thus, when a form is reset, each control's current value is reset to its initial value. If a control does not have an initial value, the effect of a form reset on that control is undefined.
When a form is submitted for processing, some controls have their name paired with their current value and these pairs are submitted with the form. Those controls for which name/value pairs are submitted are called successful controls.
HTML defines the following control types:
Authors should specify the scripting language of a push button script through a default script declaration (with the META element).
Authors create buttons with the BUTTON element or the INPUT element. Please consult the definitions of these elements for details about specifying different button types.
When a form is submitted, only "on" checkbox controls can become successful. Several checkboxes in a form may share the same control name. Thus, for example, checkboxes allow users to select several values for the same property. The INPUT element is used to create a checkbox control.
The elements used to create controls generally appear inside a FORM element, but may also appear outside of a FORM element declaration when they are used to build user interfaces. This is discussed in the section on intrinsic events. Note that controls outside a form cannot be successful controls.
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form --> <!ATTLIST FORM %attrs; -- %coreattrs, %i18n, %events -- action %URI; #REQUIRED -- server-side form handler -- method (GET|POST) GET -- HTTP method used to submit the form-- enctype %ContentType; "application/x-www-form-urlencoded" onsubmit %Script; #IMPLIED -- the form was submitted -- onreset %Script; #IMPLIED -- the form was reset -- accept-charset %Charsets; #IMPLIED -- list of supported charsets -- >
Start tag: required, End tag: required
Attribute definitions
The default value for this attribute is the reserved string "UNKNOWN". User agents may interpret this value as the character encoding that was used to transmit the document containing this FORM element.
Attributes defined elsewhere
The FORM element acts as a container for controls. It specifies:
A form can contain text and markup (paragraphs, lists, etc.) in addition to form controls.
The following example shows a form that is to be processed by the "adduser" program when submitted. The form will be sent to the program using the HTTP "post" method.
<FORM action="http://somesite.com/prog/adduser" method="post"> ...form contents... </FORM>
The next example shows how to send a submitted form to an email address:
<FORM action="mailto:Kligor.T@gee.whiz.com" method="post"> ...form contents... </FORM>
Please consult the section on form submission for information about how user agents must prepare form data for servers and how user agents should handle expected responses.
Note. Further discussion on the behavior of servers that receive form data is beyond the scope of this specification.
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required for all but submit & reset -->
<!ELEMENT INPUT - O EMPTY -- form control -->
<!ATTLIST INPUT
%attrs; -- %coreattrs, %i18n, %events --
type %InputType; TEXT -- what kind of widget is needed --
name CDATA #IMPLIED -- submit as part of form --
value CDATA #IMPLIED -- required for radio and checkboxes --
checked (checked) #IMPLIED -- for radio buttons and check boxes --
disabled (disabled) #IMPLIED -- unavailable in this context --
readonly (readonly) #IMPLIED -- for text and passwd --
size CDATA #IMPLIED -- specific to each type of field --
maxlength NUMBER #IMPLIED -- max chars for text fields --
src %URI; #IMPLIED -- for fields with images --
alt CDATA #IMPLIED -- short description --
usemap %URI; #IMPLIED -- use client-side image map --
tabindex NUMBER #IMPLIED -- position in tabbing order --
accesskey %Character; #IMPLIED -- accessibility key character --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
onselect %Script; #IMPLIED -- some text was selected --
onchange %Script; #IMPLIED -- the element value was changed --