Composition: determine NodeRole.INTERNAL by not INPUT/OUTPUT

newer documentation of NodeRole suggests INTERNAL should be determined
by not being INPUT or OUTPUT, not by not being ORIGIN or TERMINAL

psyneulink/core/compositions/composition.py

@@ -5204,7 +5204,12 @@ def _determine_node_roles(self, context=None):
           - all Nodes that have one or more InputPorts for which default_input == DEFAULT_VARIABLE
 
         INTERNAL:
-          - all Nodes that are *neither* ORIGIN nor TERMINAL
+            A `Node <Composition_Nodes>` that is neither `INPUT` nor
+            `OUTPUT`.  Note that it *can* also be `ORIGIN`, `TERMINAL`
+            or `SINGLETON`, if it has no `afferent
+            <Mechanism_Base.afferents>` or `efferent
+            <Mechanism_Base.efferents>` Projections or neither,
+            respectively. This role cannot be modified programmatically.
 
         CYCLE:
           - all Nodes that identified as being in a cycle by self.graph_processing
@@ -5473,7 +5478,7 @@ def is_output_node(node, allow_cycle=False):
         for node in self.nodes:
             if all(n in self.nodes_to_roles[node] for n in {NodeRole.ORIGIN, NodeRole.TERMINAL}):
                 self._add_node_role(node, NodeRole.SINGLETON)
-            if not any(n in self.nodes_to_roles[node] for n in {NodeRole.ORIGIN, NodeRole.TERMINAL}):
+            if not any(n in self.nodes_to_roles[node] for n in {NodeRole.INPUT, NodeRole.OUTPUT}):
                 self._add_node_role(node, NodeRole.INTERNAL)
 
         # Finally, remove any NodeRole assignments specified in excluded_node_roles