The submission of a form in a Visualforce page causes the view state and all user inputs to be processed by the controller. In the event that the form is being submitted back, purely to introduce some additional information based on a single user input, this can be inefficient, especially if there are a large number of field inputs on the page. The <apex:actionRegion /> component can be used to break the form up into discrete sections, reducing the amount of data processed by the controller and improving performance of the page.
In this recipe we will create a Visualforce page that allows a user to create a case record. The case subject is automatically generated by a controller extension from a base subject entered by the user and the name of the account that the case is associated with. A change to either the base subject or the account lookup causes the form to be submitted in order to update the generated subject. Each of these fields is contained...