Registers block as a child of self. :py:class:`Block` s assigned to self as
        attributes will be registered automatically.

def register_child(self, block, name=None):
        """Registers block as a child of self. :py:class:`Block` s assigned to self as
        attributes will be registered automatically."""
        if name is None:
            name = str(len(self._children))
        self._children[name] = block