Form (web)

A webform, web form or HTML form on a web page allows a user to enter data that is sent to a server for processing. Forms can resemble paper or database forms because web users fill out the forms using checkboxes, radio buttons, or text fields. For example, forms can be used to enter shipping or credit card data to order a product, or can be used to retrieve search results from a search engine.

Description

Forms are enclosed in the HTML <form> element. This element specifies the communication endpoint the data entered into the form should be submitted to, and the method of submitting the data, GET or POST.

Elements

Forms can be made up of standard graphical user interface elements:
* <text> — a simple text box that allows input of a single line of text.
* <email> - a type of <text> that requires a partially validated email address
* <number> - a type of <text> that requires a number
* <password> — similar to <text>, it is used for security purposes, in which the characters typed in are invisible or replaced by symbols such as *
* <radio> — a radio button
* <file> — a file select control for uploading a file
* <reset> — a reset button that, when activated, tells the browser to restore the values to their initial values.
* <submit> — a button that tells the browser to take action on the form (typically to send it to a server)
* <textarea> — much like the <text> input field except a <textarea> allows for multiple rows of data to be shown and entered
* <select> — a drop-down list that displays a list of items a user can select from

The sample image on the right shows most of these elements:
* a text box asking for your name
* a pair of radio buttons asking you to pick your sex
* a select box giving you a list of eye colors to choose from
* a pair of check boxes to click on if they apply to you
* a text area to describe your athletic ability
* a submit button to send it to the server

These basic elements provide most common graphical user interface (GUI) elements, but not all. For example, there are no equivalents to a tree view or grid view.

A grid view, however, can be mimicked by using a standard HTML table with each cell containing a text input element. A tree view could also be mimicked through nested tables or, more semantically appropriately, nested lists. In both cases, a server-side process is responsible for processing the information, while JavaScript handles the user-interaction. Implementations of these interface elements are available through JavaScript libraries such as jQuery.

HTML 4 introduced the <label> tag, which is intended to represent a caption in a user interface, and can be associated with a specific form control by specifying the id attribute of the control in the label tag's for attribute. This allows labels to stay with their elements when a window is resized and to allow more desktop-like functionality (e.g. clicking a radio button or checkbox's label will activate the associated input element).

HTML 5 introduces a number of input tags that can be represented by other interface elements. Some are based upon text input fields and are intended to input and validate specific common data. These include <email> to enter email addresses, <tel> for telephone numbers, <number> for numeric values. There are additional attributes to specify required fields, fields that should have keyboard focus when the web page containing the form is loaded, and placeholder text that is displayed within the field but is not user input (such as the 'Search' text displayed in many search input fields before a search term is entered). These tasks used to be handled with JavaScript, but had become so common that support for them was added to the standard. The <date> input type displays a calendar from which the user can select a date or date range. And the color input type can be represented as an input text simply checking the value entered is a correct hexadecimal representation of a color, according to the specification, or a color picker widget (the latter being the solution used in most browsers which support this attribute).

Submission

When data that has been entered into HTML forms is submitted, the names and values in the form elements are encoded and sent to the server in an HTTP request message using GET or POST. Historically, an email transport was also used. The default MIME type (internet media type), application/x-www-form-urlencoded, is based on a very early version of the general URI percent-encoding rules, with a number of modifications such as newline normalization and replacing spaces with "+" instead of "%20". Another possible encoding, Internet media type