Library reference Reference for classes and functions provided as built-in or extension packages. Built-in functions A built-in function is a predefined function that is part of the runtime system, or provided as a library function automatically loaded when a program starts. The built-in functions are part of the language.Utility modulesA utility function is a function provided in a separate library; it is not built in the runtime system.Built-in packagesThese topics cover the built-in classes provided by the Genero Business Development Language.Built-in front callsThis section contains the description of all built-in front calls.Extension packagesSeveral utility classes and functions are provided in additional packages.File extensionsThis page describes the file extensions used by the language.Genero BDL errorsSystem error messages sorted by error number.