A non-traditional collection of Indirect Objects making up
the content of a PDF.
This collection has some of the characteristics of an Array and
some of a Dictionary. Objects are referred to by index - starting
at zero - like an Array. However they do not move within the list
because they are identified by index - like a Dictionary with
We call this type of hybrid object a Soup. We assign it
traditional interfaces to make it easier to use.
IEnumerable<IndirectObject>, IList, ICollection, IEnumerable,