':returns: a reference to the list containing one or more elements that
were added via `append_element`
:raises AssertionError: if result was not set or value is incompatible
with `append_element`'

@property
def elements(self):

    assert self._ready, '_CallbackResult    was    not    set'
    assert (isinstance(self._values, list) and (len(self._values) > 0)), ('_CallbackResult    value    is    incompatible    with    append_element:    %r' % (self._values,))
    return self._values
