I think it might be some internal syntax. When looking at processes, the %objlasterr value often has errors in that syntax: 

I edited out the namespace and classname for privacy. But the first and third marks are the namespace, the 2nd and 4th are the class.

Also, to make clear, no this isn't my code, it's in the error message being returned by the HS Compiled Routine. I imagine it's part of the internal workings. But I'm really trying to figure out how to get that ^%ISCLOG part to actually log.