else if (node->node_group) /* enter level group (step down into tree) */
return getFirstValidLevelSeries(node->node_group);
else if (node->parent_link) /* skip start entry of level group */
else if (node->node_group) /* enter level group (step down into tree) */
return getFirstValidLevelSeries(node->node_group);
else if (node->parent_link) /* skip start entry of level group */