Building blocks of a form controller

• Inputs are the building blocks of a form. So, a typical form consists of a header, a note/description about the form, and a collection of different inputs and actions.
• In the membership form example that we see here, the header of the form is membership form, and then we have a description that says that the form is for upgrading or downgrading a visitor's membership.
• Then, we have inputs like customer name, email, country, membership type,etc.
• And once these inputs are entered we perform an action - this can either be submit or cancel.

Operational flow of the form controller

• When a button in the widget is clicked, a form can be opened as a result of the widget's action handler.
  
• The change handler will be executed if the value of an input is changed when there is "trigger_on_change" set in certain inputs. The change handler can be used to either add, remove or update fields in the form depending on the input made for a certain field. 
• The dynamic field handler is executed when the text is entered in the dynamic_select input. The input is used to show dynamic options in a dropdown on demand.
• Then, the submit handler of a form controller is invoked on form submission and form cancellation (if required).