Explicitly don’t document the base Widget class.

packages/schema/generate-spec.py

@@ -45,7 +45,7 @@ def typing(x):
  elif isinstance(x, Instance) and issubclass(x.klass, widgets.Widget):
  s = 'reference to %s widget'%(x.klass.__name__)
  # ADD the widget to this documenting list
- if x.klass not in [i[1] for i in widgets_to_document]:
+ if x.klass not in [i[1] for i in widgets_to_document] and x.klass != widgets.Widget:
  widgets_to_document.append((x.klass.__name__, x.klass))
  elif isinstance(x, Any):
  # In our case, these all happen to be values that are converted to strings