This is used for generating docs so a nested RNA struct such as MaterialRaytraceTransparency are listed under Material rather then in the global struct list)
These RNA structs are used for grouping properties and don't correspond to a C structure.
* errors in python called operators are raised as errors
* Python defined operators errors are reported as errors (not full traceback yet)
* added BKE_reports_string, same as BKE_reports_print but it returns a string rather then printing it.
* WM_operator_name_call optionally takes an initialized report struct
