Which alphabet - English, Cryllic, Katakana, or Hebrew? Sometimes I've accepted only valid base-64 characters for transport reasons - RFC 4648. Other times onl

Which alphabet - English, Cryllic, Katakana, or Hebrew? Sometimes I've accepted only valid base-64 characters for transport reasons - RFC 4648. Other times only email characters - RFC 5322. A couple of times I was limited to the restrictions of the underlying OS or platform. Some runtimes are ascii-centric and require extra care dealing with unicode or extended characters. IBM mainframes / gateways can have endian issues. And sometimes it's just trivial - reusing a regex from a previous project - for example. EDIT: wrong word in first line.