Get the string value stored in the object, or convert the value
in the object to a string of that length if it is of a different type.
It is overloaded as stringValue().
Nodes of different colours represent the following:
Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.