Form modules are one of the two fundamental types of modules in FCAS. They are an essential part of almost any application that you create in FCAS. They contain all the procedures that are assigned to forms and the fields on the forms. FCAS lets you write event procedures which are run when users trigger any of an array of events for a field or the form itself. Each field type has a variety of event procedures that can execute BASIC code. For example, you can program the Click() procedure of a button to open a new window, or you can program the Change() method of a text field, which runs when the information contained in the field changes, to validate the new information. Simple FCAS applications may use only a single form module. However, as a project grows, it may become necessary to add additional forms. If there are procedures that are used in more than one form, or are called from different fields on the same form, it may become necessary to put these procedures in a code module.