Build::Hopen::G::Entity - The base class for all hopen nodes and edges
hopen creates and manages a graph of entities: nodes and edges. This class holds common information.
The name of this entity. The name is for human consumption and is not used by hopen to make any decisions. However, node names starting with an underscore are reserved for hopen's internal use.
'0' (a single digit zero) is forbidden (since it's falsy).