Lay out new client structure

cheuph/message_tree_widget.py

@@ -0,0 +1,26 @@
+__all__ = ["MessageTreeWidget"]
+
+class MessageTreeWidget:
+    """
+    This widget displays an ElementSupply, including user interface like a
+    cursor or folding markers. It usually is part of a RoomWidget. It also
+    keeps a RenderedMessageCache (and maybe even other caches).
+
+    It receives key presses and mouse clicks from its parent widget. It
+    receives redraw requests and cache invalidation notices from the
+    RoomWidget.
+
+    It doesn't directly receive new messages. Rather, the RoomWidget adds them
+    to the ElementSupply and then submits a cache invalidation notice and a
+    redraw request.
+
+    It emits a "room top hit" event (unnamed as of yet). When the RoomWidget
+    receives this event, it should retrieve more messages from the server.
+
+    It emits a "edit" event (unnamed as of yet) when the user attempts to edit
+    a message. When the RoomWidget receives this event, it should open a text
+    editor to compose a new message, and send that message once the user
+    finishes editing it.
+    """
+
+    pass