Tree::DAG_Node is a (super)class for representing nodes in a tree. 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).