Add an additional function that should be implemented.

wrappers/modelverse.py

@@ -999,3 +999,7 @@ def element_list_nice(model_name):
 def connections_between(model_name, source_element, target_element):
     """Gets a list of all allowed connections between the source and target element in the model."""
     raise NotImplementedError()
+
+def define_attribute(model_name, node, attr_name, attr_type):
+    """Create a new attribute, which can be instantiated one meta-level below."""
+    raise NotImplementedError()