BRK on the BBC Micro & Acorn Electron

In the operating system for the BBC Micro (& Acorn Electron), the standard is to write BRK followed by an error number, then the error message ending with a 0

1BRK           ; Software break
2EQUB 0        ; Error code
3EQUS "Silly"  ; This is a real error message in BBC BASIC, try: AUTO10,1000
4EQUB 0        ; End of message marker

Service ROM's usually write error messages into RAM starting at &0100 and then do a JMP &0100 to run it. They do that as the handler is usually in a Language rom so they would be paged out if they ran BRK from their own ROM.