-Specifies a file containing a message that is displayed before the boot
-prompt. [CURRENTLY UNIMPLEMENTED]
+Specifies a file containing a message that is displayed before the
+boot prompt. You may specify either a plain pathname, in which case
+the default device and partition will be derived from the
+\fIdevice=\fR and \fIpartition=\fR lines in the global section of
+\fByaboot.conf\fR, or you can specify a full OpenFirmware device path.
+The message file must be plain ASCII text with UNIX newlines. Note:
+only the first 2000 bytes of this file will be read.