PSDExpansionByRegionsParameter is an option for
PSDCreatePythonScripts and other functions of the pySecDec
interface. It specifies the small parameter in which the given loop
integral will be expanded using the method of regions. The default value
is None, meaning that no expansion takes place.
The order up to which the expansion should be carried out must be
specified via the option PSDExpansionByRegionsOrder.
Overview, PSDCreatePythonScripts.