Added documentation to clarify attachments

README.md

@@ -169,6 +169,7 @@ would be channels in Discord and IRC.
 
 -   ServerMessageSender (optional): adds message sending capability.
 -   ServerMessageSendCompleter (optional): adds message input completion capability.
+-   ServerMessageAttachmentSender (optional): adds attachment sending capability
 -   ServerMessageEditor (optional): adds message editing capability.
 -   ServerMessageActioner (optional): adds custom actions capability.
 -   ServerMessageUnreadIndicator (optional): adds unread indication capability.
@@ -269,6 +270,7 @@ The frontend could implement this interface and check if incoming
 #### Interfaces (only known)
 
 -   MessageNonce (optional)
+-   SendableMessageAttachments (optional): adds attachments into the message
 
 
 

cchat.go

@@ -230,7 +230,12 @@ type ServerMessageSender interface {
 	SendMessage(SendableMessage) error
 }
 
+// ServerMessageAttachmentSender optionally extends ServerMessageSender to
+// indicate that the backend can accept attachments in its messages. The
+// attachments will still be sent through SendMessage, though this interface
+// will mostly be used to indicate the capability.
 type ServerMessageAttachmentSender interface {
+	ServerMessageSender
 	// SendAttachments sends only message attachments. The frontend would
 	// most of the time use SendableMessage that implements
 	// SendableMessageAttachments, but this method is useful for detecting