Classes implementing IGoCollection need not maintain an indexing of its objects--in other words, they need not implement an IList of GoObject. But at any one time each collection implementing this interface should maintain an ordering of all of its items, so that the enumerator will iterate "forwards" over the list, and so that the Backwards enumerable's enumerator will iterate "backwards" over that list. This ordering should be guaranteed to remain stable as long as the collection is unchanged. However, a call to Add or Remove may cause the ordering of the items to be altered.

Reference

IGoCollection Members
Northwoods.GoWeb Namespace
GoCollection Class
GoDocument Class
GoLayer Class
GoGroup Class