'Iterates over all subviews from collections at this view from
*all* sources. If the object for this view in any source is not
iterable, then a ConfigTypeError is raised. This method is
intended to be used when the view indicates a list; this method
will concatenate the contents of the list from all sources.'

def all_contents(self):

    for (collection, _) in self.resolve():
        try:
            it = iter(collection)
        except TypeError:
            raise ConfigTypeError(u'{0}    must    be    an    iterable,    not    {1}'.format(self.name, type(collection).__name__))
        for value in it:
            (yield value)
