Create a ``desc`` node summarizing the config attribute

        The ``config`` attribute is not statically available from a task class.
        This method manually creates a signature and docstring for the
        config attribute.

def _format_config_nodes(self, modulename, classname):
        """Create a ``desc`` node summarizing the config attribute

        The ``config`` attribute is not statically available from a task class.
        This method manually creates a signature and docstring for the
        config attribute.
        """
        fullname = '{0}.{1}.config'.format(modulename, classname)

        # The signature term
        desc_sig_node = desc_signature()
        desc_sig_node['module'] = modulename
        desc_sig_node['class'] = classname
        desc_sig_node['fullname'] = fullname

        prefix = 'attribute'
        desc_sig_node += desc_annotation(prefix, prefix)
        desc_sig_name_node = desc_addname('config', 'config')
        # Fakes the look of a cross reference.
        desc_sig_name_node['classes'].extend(['xref', 'py'])
        desc_sig_node += desc_sig_name_node

        # The content is the one-sentence summary.
        summary_text = (
            'Access configuration fields and retargetable subtasks.'
        )
        content_node_p = nodes.paragraph(text=summary_text)
        content_node = desc_content()
        content_node += content_node_p

        desc_node = desc()
        desc_node['noindex'] = True
        desc_node['domain'] = 'py'
        desc_node['objtype'] = 'attribute'
        desc_node += desc_sig_node
        desc_node += content_node
        return desc_node