Plan 9 - man page for error (plan9 section 5)

ERROR(5)			       File Formats Manual				 ERROR(5)

NAME
       error - return an error

SYNOPSIS
       Rerror tag[2] ename[64]

DESCRIPTION
       The  Rerror  request  (there is no Terror) is used to return an error string, of length 64
       (ERRLEN in <libc.h>), describing the failure of a transaction.	It  replaces  the  corre-
       sponding  reply	message  that  would  accompany a successful call; its tag is that of the
       request.

											 ERROR(5)