Satellite Forms also includes support for an extensible control architecture (similar to Visual Basic's ActiveX components). Custom Satellite Forms controls can be built using C and the Satellite Forms Extension (SFX) API. The SFX API could be used to build printing or serial communications functionality into an application. It could also be used to build custom graphical user interface controls (such as a mapping component for geographic applications or a grid control for tabular data display). Documentation and complete SFX API is included when the product is installed.