Systems and methods are disclosed in which a self-describing file is generated and utilized to provide applications with the ability to properly preserve unknown file content. A self-describing file may contain, or be associated with, an extension section that provides information that an application can use to properly calculate unknown file content. The extension section may include functions of formulas that the application can use to calculate values for data that the application would not otherwise support. This allows for the content of the self-describing file to be modified by an application that does not support all of the capabilities of the file while maintaining the integrity of the file and user experience when the file is subsequently accessed by a full featured application.