When you run an application, the Application Express engine relies on two processes:
When you request a page using a URL, the engine is running Show Page.
Show Page is the page rendering process. It assembles all the page attributes (including regions, items, and buttons) into a viewable HTML page.
Accept Page performs page processing. It performs any computations, validations, processes, and branching.
When you submit a page, the Application Express engine is running Accept Page or performing page processing during which it saves the submitted values in the session cache and then performs any computations, validations, or processes.