Updated explanation.

doc/ssl/SSL_CTX_set_cipher_list.pod

@@ -34,9 +34,22 @@ a necessary condition. On the client side, the inclusion into the list is
 also sufficient. On the server side, additional restrictions apply. All ciphers
 have additional requirements. ADH ciphers don't need a certificate, but
 DH-parameters must have been set. All other ciphers need a corresponding
-certificate and key. A RSA cipher can only be chosen, when a RSA certificate is
-available, the respective is valid for DSA ciphers. Ciphers using EDH need
-a certificate and key and DH-parameters.
+certificate and key.
+
+A RSA cipher can only be chosen, when a RSA certificate is available.
+RSA export ciphers with a keylength of 512 bits for the RSA key require
+a temporary 512 bit RSA key, as typically the supplied key has a length
+of 1024 bit. RSA ciphers using EDH need a certificate and key and
+additional DH-parameters.
+
+A DSA cipher can only be chosen, when a DSA certificate is available.
+DSA ciphers always use DH key exchange and therefore need DH-parameters.
+
+When these conditions are not met for any cipher in the list (e.g. a
+client only supports export RSA ciphers with a asymmetric key length
+of 512 bits and the server is not configured to use temporary RSA
+keys), the "no shared cipher" (SSL_R_NO_SHARED_CIPHER) error is generated
+and the handshake will fail.
 
 =head1 RETURN VALUES