docs: update controller api design

diff --git a/docs/design/part-controller.txt b/docs/design/part-controller.txt
index c75da54..1a2f23e 100644 (file)
--- a/docs/design/part-controller.txt
+++ b/docs/design/part-controller.txt
@@ -34,3 +34,7 @@ generate various repetitive signals. Those can be made more complex by chaining
 the control sources. One can attach another control-source to e.g. modulate the
 frequency of the first GstLFOControlSource.
 
+In most cases GstControlBindingDirect will be the binding to be used. Other
+control bindings are there to handle special cases, such as having 1-4 control-
+sources and combine their values into a single guint to control a rgba-color
+property.