def get_layers(self, class_: Type[L], became: bool=True) -> List[L]:
out = self._index.get(class_, [])<EOL>if became:<EOL><INDENT>out += self._transformed.get(class_, [])<EOL><DEDENT>return out<EOL>
Returns the list of layers of a given class. If no layers are present
then the list will be empty.

:param class_: class of the expected layers
:param became: Allow transformed layers in results