I've been working with ECMA2s recently and I've just started to need a multi-valued attribute as part of the object schema.
Working with this, I had a problem trying to populate this attribute during an Import run.
Typically dealing with multi-valued attributes strategies in the past involves iterating through each value using a For Each... loop or something similar. The issue I was running into was how to designate the index on the multi-valued attribute. I couldn't find much on the web either.
For ECMA2 schemas I figured out an easy to populate the attribute. Place the value(s) in a List (of Object) type then you can populate the multi-valued attribute with the List.
Here's a little code showing what I mean:
Dim groups As List(Of Object) = New List(Of Object)
'populate groups with values as needed
Hope this helps.