A revised version of XForms 1.0 incorporating new material on the XForms Processing Model has been released by the W3C XForms Working Group. The working draft document "presents a description of the architecture, concepts, processing model, and terminology underlying XForms, the next generation Web forms. 'XForms' is W3C's name for a specification of Web forms that can be used with a wide variety of platforms of varying capabilities, for instance, desktop computers, television sets, personal digital assistants, cell phones, computer peripherals and even paper."
Reference: W3C Working Draft 16-February-2001, edited by Micah Dubinko (Cardiff), Josef Dietl (Mozquito Technologies), Roland Merrick (IBM), Dave Raggett (W3C/OpenWave), T. V. Raman (IBM), and Linda Bucsay Welsh (Intel). This WD revision supersedes the previous working draft of 2000-12-19.
Appendix A 'Schema for XForms Model' defines "the schema for the XForm <model> element, and everything contained in it. This includes the XForms defined data types, and XForms specific properties whose values are dynamic, and may may change at runtime. It also contains a definition of the XForms Simple Syntax elements, which can be used as an alternative to XML syntax, for defining the XForms model's elements."
Dynamic Constraints: "Many forms define integrity constraints that act over multiple fields. For example, the total value of an order can be defined in terms of a computation over other values such as unit prices, quantities, discounts, and tax and shipping costs. Such computations can be conveniently represented using the syntax outlined in here. This chapter  describes an XForms Dynamic Constraints Language (DCL) based on XPath that enables these types of expressions without the use of a separate scripting language. Dynamic Constraints are also useful for declaratively stating when a form control or subform needs to be filled out, according to some other value. A further use is to functionally define the acceptable choices for some form control, when this depends on other values.
Background: "Forms are an important part of the Web, and they continue to be the primary means of interactivity used by many Web sites. Web applications and eCommerce solutions have sparked the demand for better Web forms with richer interactions. XForms are the response to this demand -- extended analysis, followed by the creation of a new platform-independent markup language for online interaction between a XForms Processor and a remote entity. XForms are the successor to XHTML forms, and benefit from the lessons learned in the years of HTML forms implementation experience."
"The current design of Web forms doesn't separate the purpose from the presentation of a form. XForms, in contrast, are comprised of separate sections that describe what the form does, and how the form looks. This allows for flexible presentation options, including classic XHTML forms, to be attached to an XML form definition. Key goals of the XForms design activity include: "Support for handheld, television, and desktop browsers, plus printers and scanners; Richer user interface to meet the needs of business, consumer and device control applications; Decoupled data, logic and presentation; Improved internationalization; Support for structured form data; Advanced forms logic; Multiple forms per page, and pages per form; Suspend and Resume support; Seamless integration with other XML tag sets."