... IRUT (Internet Routable Unique Token) is a 22-character string that's a modified base64 encoding of a 128-bit v4 UUID that replaces base64 character '/' with '_' and '+' with '-'. This makes it simple to use IRUT inside URL/URI per RFC 3986. And, is mostly suitable for Linux and Windows file/directory naming... It's mostly except if the IRUT begins with '-' '--' etc
This is legal per IRUT but is annoying because many Linux command assume a valid IRUT such as "-GSSwHkeSJ24e2kfpXle_g" is a command line option.
I think this is just a documentation thing. Probably best to prefix file/directory names w/a short valid string to avoid the issue.