Overview of extension modules
Users and developers are free to implemented functionality C extensions to Python in order to increase speed. In the current framework some functionality that a user is required to customize for model specification is necessarily implemented via extension modules, whilst custom functionality can optionally be written in extension modules.
Not all extension modules are documented yet. A subset of extension modules are considered as reserved for internal usage, being accessed indirectly by users through Python-exposed classes in the modeling language. Wrapping these extension modules conceals lower-level handling of operations that the user need not worry about: this part of the framework is less flexible because the operations dominate likelihood function evaluation cost, and it is more difficult to develop the source code whilst maintaining performance. The extensions documented here are readily transplanable with other custom code, be it extension modules or otherwise as appropriate for defining a custom model, and in most cases should not have a substantial effect on overall speed.