diff --git a/docs/api.rst b/docs/api.rst
index c1139d8..8ac93c8 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -32,6 +32,10 @@ General Section
   Raspberry Pi is so slow that multiple connections don't help much, since the
   CPU and not the network is the bottleneck.
 
+- ``collections``: Optional, a comma-separated list of collections to
+  synchronize. If this parameter is omitted, it is assumed the storages are
+  already directly pointing to one collection each.
+
 .. _pair_config:
 
 Pair Section