Form (web) - Description

Description

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

Forms can be made up of standard graphical user interface elements:

• text input — a simple text box that allows input of a single line of text (an alternative, password, is used for security purposes, in which the characters typed in are invisible or replaced by symbols such as *)
• checkbox — a check box
• 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 all 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 combo box, 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.

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 credit card numbers and security codes. 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.) The date input type displays a calendar from which the user can select a date or date range.

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 multipart/form-data, is also available and is common for POST-based file submissions.