+
+
+# Perhaps surprisingly, used to indicate that an account name is
+# invalid.
+class InvalidAccountError < StandardError
+end
+
+
+# Used to indicate that an account does not exist on the filesystem.
+class NonexistentAccountError < StandardError
+end
+
+
+# Used to indicate that a domain does not exist on the filesystem.
+class NonexistentDomainError < StandardError
+end