Returns a nested list of Philippine provinces, grouped into super-regions (Luzon, Visayas, Mindanao), and then by regions (Region I, II, III, etc). Most Filipinos will be more familiar with the province that a given city belongs to rather than its region number, so a more appropriate list to display is the one generated by the preceeding /provinces call.

It's a good idea to cache this information, as this data is largely static.