tracking), but allows loading external resources when reading
from NNTP newsgroups and the like.
+People controlling these external resources won't be able to tell
+that any one person in particular has read the message (since
+it's in a public venue, many people will end up loading that
+resource), but they'll be able to tell that somebody from your IP
+address has accessed the resource.
+
This can also be a function to be evaluated. If so, it will be
called with the group name as the parameter, and should return a
regexp."