topo (default) — topological; top-level consumers first, dependencies below.
revtopo — reversed; foundations first, consumers last.
alpha — alphabetical by layer name.
ruleset — exactly as written in the structarmed.php ruleset.
network-simplex (default) — balances edge lengths; usually the cleanest, fewest crossings.
tight-tree — packs nodes into a compact tree.
longest-path — strictest layering by dependency depth; exaggerates tall stacks.