The graph file was generated automatically from a session with the LDBX graphical interface to the standard DBX debugger. Nodes are drawn with the 'record' shape. Labels of this shape are interpreted specially as nested horizontal and vertical box lists formatted as tables. In a record label, curly braces { } enclose lists, vertical bar | separates list items, and creates a port identifier for attaching edges. Edges are also labeled with 'id' attributes. Though not demonstrated in this particular file, these attributes allow referencing multiple (parallel) edges between the same node pair.