Improve documentation of ssl_set_mtu().
@@ -1392,18 +1392,25 @@ void mbedtls_ssl_set_bio( mbedtls_ssl_context *ssl,
* example when a PMTU estimate becomes available from other
* sources, such as lower (or higher) protocol layers.
*
- * \note This only controls the size of the packet we send.
+ * \note This only controls the size of the packets we send.
* Client-side, you can request the server to use smaller
* records with \c mbedtls_ssl_conf_max_frag_len().
*
* \note If both a MTU and a maximum fragment length have been
- * configured (or negotiated with the peer), the lower limit
- * is used.
+ * configured (or negotiated with the peer), the resulting
+ * lower limit (after translating the MTU setting to a limit
+ * on the record content length) is used.
*
- * \note Values larger than #MBEDTLS_SSL_OUT_CONTENT_LEN have no
- * effect. This can only be used to decrease the maximum size
- * of datagrams sent. Values lower than record layer expansion
- * are ignored.
+ * \note This can only be used to decrease the maximum size
+ * of datagrams sent. It cannot be used to increase the
+ * maximum size of records over the limit set by
+ * #MBEDTLS_SSL_OUT_CONTENT_LEN.
+ *
+ * \note Values lower than the current record layer expansion will
+ * result in an error when trying to send data.
+ *
+ * \note Using record compression together with a non-zero MTU value
+ * will result in an error when trying to send data.
*
* \param ssl SSL context
* \param mtu Value of the path MTU in bytes
