diff --git a/proto/protocol.xml b/proto/protocol.xml
index ce1ab5f..58bf630 100644
--- a/proto/protocol.xml
+++ b/proto/protocol.xml
@@ -586,6 +586,17 @@
         capabilies and an EIS implementation may then create device based on the bound
         capabilities.
 
+        Note that seat capabilities only represent a mask of possible capabilities on
+        devices in this seat. A capability that is not available on the seat cannot
+        ever be available on any device in this seat. For example, a seat that only has the
+        pointer and keyboard capabilities can never have a device with the touchscreen
+        capability.
+
+        It is up to the EIS implementation to decide how many (if any) devices with any given
+        capability exist in this seat.
+
+        Capabilities are only advertised once and are constant for the lifetime of the seat.
+
         It is a protocol violation to send this event after the ei_seat.done event.
       </description>
       <arg name="capabilities" type="uint32" enum="ei_device.capabilities" summary="the seat capabilities"/>