XForms

XForms is a W3C specification for building web forms that aims to improve beyond traditional HTML forms by providing a clear separation of data, user interface, and submission logic. It relies on XML to define the form structure and data, and it emphasizes declarative data modeling, validation, and dynamic behavior.

The core architecture consists of three parts: the data instance, the form model, and the user interface. The instance is an XML document that holds the form data. The model (xforms:model) contains xforms:instance(s) and xforms:bind elements, which declare data types, constraints, calculations, and event-driven rules. The user interface is composed of a set of XForms controls such as xforms:input, xforms:select1, xforms:textarea, xforms:group, and xforms:repeat, which are bound to the data through the bindings and can be arranged dynamically.

Validation, constraints, and calculations are defined within the binding layer. Each input control can specify constraints, requiredness, and data types, and can derive values from expressions via calculate. The relevant attribute can govern dynamic visibility or enabling of UI elements. This architecture enables data-driven forms, conditional logic, and reusable form components without extensive client-side scripting.

Submission and data transport are handled through xforms:submission elements, which describe endpoints, methods (such as HTTP POST or GET), and data serialization. Submissions can be triggered by actions or automatically when certain conditions are met.

Historically, XForms gained attention as a robust alternative to HTML forms but received limited native browser support, leading to reliance on form processors, server-side components, or specialized engines. It remains in use in certain data-collection and enterprise environments, notably in mobile data capture and forms platforms that leverage its declarative, model-driven approach.