doc: Another addendum to Interfaces docs

diff --git a/doc/modem-api.txt b/doc/modem-api.txt
index 444e83e..e242bd1 100644 (file)
--- a/doc/modem-api.txt
+++ b/doc/modem-api.txt
@@ -130,6 +130,13 @@ Properties boolean Powered [readwrite]
                                org.ofono.TextTelephony
                                org.ofono.VoiceCallManager
 
+                       It is possible for extension interfaces (e.g. APIs
+                       that are not part of the oFono standard API) to be
+                       available in this list.  Also note that child object
+                       interfaces, such as org.ofono.Message,
+                       org.ofono.VoiceCall, org.ofono.NetworkOperator,
+                       will never be part of this list.
+
                        Please note that the set of Interfaces can and does
                        change frequently (e.g. due to change in Powered
                        and Online properties.)  If a given interface is no