Recently I came across the necessity of converting Islamic hijrī dates to Gregorian dates in order to automatically harvest data from the Baṣbakanlik Osmanli Arṣivi’s catalogue into my research database. Unfortunately the database I use (the reference manager Sente) is proprietary software that can only deal with Gregorian dates. Thus, I needed to translate a certain string through XSLT in order to produce the correct XML for import into the database. I soon discovered that even though, formally the specifications for the format-date() function in XPath 2.0 include the hijrī calendar (labelled “Islamic”) and even Arabic month names, this specification was never actually implemented. As I could not find any available code on the net, I adopted the javascript conversion between Gregorian, Julian, and Hijri calendars provided by John Walker’s Calendar Converter for XSLT 2.0 and decided to share the functions on GitHub for reuse.