Handle 'must be indirect reference' constraints in spec

[dwarring]

A generic mechanism may be necessary to handle the 'must be an indirect reference; constraint on certain entries. For example the threads entry in the Catalog object see [PDF 1.7 TABLE 3.25 Entries in the catalog dictionary].

Most likely the entry trait (Dictionaries) and index trait Arrays needs an additional :ind-ref argument that is somehow interpreted during Dict/Array AST constructions and/or passed-through to the serializer. so that it 'knows' to construct an indirect object.