Description:

Suppose you have a class (like Food::Fish::Fishstick) that is derived, via its @ISA, from
one or more superclasses (as Food::Fish::Fishstick is from Food::Fish, Life::Fungus, and Chemicals),
and some of those superclasses may themselves each be derived, via its @ISA, from one or
more superclasses (as above).
When, then, you call a method in that class ($fishstick->calories), Perl first searches
there for that method, but if it's not there, it goes searching in its superclasses,
and so on, in a depth-first (or maybe "height-first" is the word) search.
In the above example, it'd first look in Food::Fish, then Food, then Matter,
then Life::Fungus, then Life, then Chemicals.
This library, Class::ISA, provides functions that return that list -- the list (in order)
of names of classes Perl would search to find a method, with no duplicates.