get_version_number documentation: explicitly mention VERSION_UNKNOWN
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index a4d0dde..a2b4cdd 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -4088,6 +4088,10 @@
* \brief Return the (D)TLS protocol version negotiated in the
* given connection.
*
+ * \note If you call this function too early during the initial
+ * handshake, before the two sides have agreed on a version,
+ * this function returns #MBEDTLS_SSL_VERSION_UNKNOWN.
+ *
* \param ssl The SSL context to query.
* \return The negotiated protocol version.
*/