Is this really the version you are looking for? Kentico Xperience 12 Service Pack Documentation is no longer updated. Use the switcher in the header to choose your product version.
Form controls provide the interface for the editing forms that allow users to input data in Kentico, both in the administration interface and on the pages of Portal Engine sites. Each form control represents a single field, and displays a certain form element, such as a text box for user input, a group of radio buttons, a selector etc.
You can insert form controls into all editing forms that are based on the Kentico form engine, including the following:
Form controls are implemented as standard ASP.NET controls using one of the following approaches:
In both cases, the control class must inherit from the CMS.FormEngine.Web.UI.FormEngineUserControl class.