From Version 3.6
When a page is created an 'extras' file is also created. It can be accessed and edited in Admin/pages 'Get extras'. The extras file is displayed by adding a dollar synbol $ to the first line of the page text (or hidden by removing the symbol).
The extras file text is not auto-formatted into paragraphs like normal page content so HTML paragraph tags should be used to write paragraphs.
The 'extras' feature might be useful, for example, with a standard block of HTML such as an online shopping form with an 'Add to basket' button that can be turned on or off or adjusted without needing to re-create it each time.