XForms - Differences From HTML Forms

Differences From HTML Forms

In contrast to the original HTML forms, the creators of XForms have used a model–view–controller approach. The model consists of one or more XForms models describing form data, constraints upon that data, and submissions. The view describes what controls appear in the form, how they are grouped together, and what data they are bound to. CSS can be used to describe a form's appearance.

An XForms document can be as simple as an HTML form (by only specifying the submission element in the model section, and placing the controls in the body), but XForms includes many advanced features. For example, new data can be requested and used to update the form while it is running, much like using XMLHttpRequest/AJAX except without scripting. The form author can validate user data against XML Schema data types, require certain data, disable input controls or change sections of the form depending on circumstances, enforce particular relationships between data, input variable length arrays of data, output calculated values derived from form data, prefill entries using an XML document, respond to actions in real time (versus at submission time), and modify the style of each control depending on the device they are displayed on (browser versus mobile versus text only, etc.). There is often no need for any scripting with languages such as JavaScript. However, XForms does include an event model and actions for implementing more complex form behaviors. Actions and event handling are specified using the XForms XML dialect rather than more common scripting languages like JavaScript.

Like HTML forms, XForms can use various non-XML submission protocols (multipart/form-data, application/x-www-form-urlencoded), but a new feature is that XForms can send data to a server in XML format. XML documents can also be used to prefill data in the form. Because XML is a standard, many tools exist that can parse and modify data upon submission, unlike the case with legacy forms where in general the data needs to be parsed and manipulated on a case by case basis. XForms is itself an XML dialect, and therefore can create and be created from other XML documents using XSLT. Using transformations, XForms can be automatically created from XML schemas, and XForms can be converted to XHTML forms.