Any files encoded as emacs-mule using oc-unicode won't be read
correctly by Emacs 21.
+* Using epop3.el package causes Emacs to signal an error.
+
+The error message might be something like this:
+
+ "Lisp nesting exceeds max-lisp-eval-depth"
+
+This happens because epop3 redefines the function gethash, which is a
+built-in primitive beginning with Emacs 21.1. We don't have a patch
+for epop3 that fixes this, but perhaps a newer version of epop3
+corrects that.
+
* On systems with shared libraries you might encounter run-time errors
from the dynamic linker telling you that it is unable to find some
shared libraries, for instance those for Xaw3d or image support.