Internal Program Version: Tree::DAG_node  1.32.5.38.2

This class encapsulates/makes/manipulates objects that represent nodes in a
tree structure. The tree structure is not an object itself, but is emergent
from the linkages you create between nodes. This class provides the methods
for making linkages that can be used to build up a tree, while preventing
you from ever making any kinds of linkages which are not allowed in a tree
(such as having a node be its own mother or ancestor, or having a node have
two mothers).

https://metacpan.org/release/Tree-DAG_Node