Reference Data and Helpers for Small Island States and Territories // A curated reference list of countries and territories with classifications for Small Island Developing States (SIDS), sub-national island jurisdictions (SNIJ), World Bank region and income group, and political association. Sub- sovereign cases such as Aruba, Curacao, Bonaire, Sint Maarten, the French overseas territories, and Aaland Islands are represented with disambiguating codes that standard country- code packages often collapse or omit. Provides predicate helpers and a tidy joiner intended to extend rather than replace 'countrycode'. Source data is maintained at https://github.com/University-of-Aruba/island-research- reference-data and licensed CC BY 4.0.