+.SS "Profile Lookup"
+After consulting .mh_profile,
+some programs read an optional profile specified by a
+program-specific environment variable,
+and then the system-wide profile %nmhetcdir%/mhn.defaults.
+These programs are mhbuild, mhshow, mhstore, and mhn.
+mhfixmsg is similar, but has no optional profile.
+
+The first occurrence of a component is used,
+e.g.\& .mh_profile's trumps $MHSHOW's.
+A component with no value still stops further occurrences being used,
+but is considered absent.