Like an array, a collection associates a set of objects or values as a logical group and provides access to them by index. However, most collection objects are read-only. You do not assign objects to them yourself—their contents update automatically as objects are created or deleted.
The index numbering of a collection starts with 1, not 0.
Object Reference Description
ItemCollection “ItemCollection object” All of the items (imported files, folders, solids, and so on) found in the Project panel.
LayerCollection “LayerCollection object” All of the layers in a composition.
OMCollection “OMCollection object” All of the Output Module items in the project.
RQItemCollection “RenderQueueItem object” All of the render-queue items in the project.
length The number of objects in the collection.
 Retrieves an object in the collection by its index number. The first object is at index 1.