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 to be included with the IMPORT instruction.File extensionsThis page describes the file extensions used by the language.Genero BDL errorsSystem error messages sorted by error number.