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 functions A utility function is a function provided in a separate library; it is not built in the runtime system. Built-in packages These topics cover the built-in classes provided by the Genero Business Development Language. Built-in front calls This section contains the description of all built-in front calls. Extension packages Several utility classes and functions are provided in additional packages to be included with the IMPORT instruction. File extensions This page describes the file extensions used by the language. Genero BDL errors System error messages sorted by error number.