I use this for a hierarchical series type: Pern.Dragonriders
AND
A older, stupid device that only uses file/folder names (and sorting)
Code:
strcat(\nsubstr(field(\'series\'), 0, 1),template("-series/{series:subitems(0,1)||/}{series:subitems(1,2)||/}{series_index:0>5.2f}-{title}_{authors}_{id}")\n)