The loop driver declaration has the form looper name, where name is any identifier. When the compiler processes the driver statement, it looks in its library directory for a file called name.drv_lang, where lang is c, f77, or f90. It then simply includes this file into the generated source.
There are currently two predefined loopers: iterative and standard. The iterative looper makes an initial guess at the advanced grid function values, then calls the update routines and iterates until the norm of the residual is below a threshold. The standard driver just calls the update routines.