This module defines abstract superclasses for tree components. Nexml defines trees as a sequence of nodes, zero or one root edge and a sequence of edges. There are different concrete instances of edges, namely those with lengths formatted as integers, and lengths formatted as floating point numbers.

In addition, there are different types of trees: those where nodes have an in-degree of 1 - true trees - and those with in-degree that can exceed 1 - networks. The AbstractNode superclass is what concrete nodes inherit from by restriction. It represents a node element much like that of GraphML, i.e. an element that is connected into a tree by edge elements. The AbstractEdge superclass is what concrete edges inherit from by restriction. It represents an edge element much like that of GraphML, i.e. an element that connects node elements. Edge The AbstractRootEdge complex type is a superclass for the edge that leads into a root, i.e. an edge with only a target attribute, but no source attribute. This type of edge is used for coalescent trees, where the initial lineage has a certain length before things start splitting up. The AbstractTree superclass is what a concrete tree inherits from. The AbstractNetwork superclass is what a concrete network inherits from. The AbstractTrees superclass is what concrete trees inherit from.