You'll have to set the backing type for your property, something like this

[BackingType(typeof(PropertyDictionaryMultiple))]
public virtual IEnumerable<string> MultipleValue { get; set; }

How would I set up a custom editor then using that as the backing type?  I tried EditorDescriptor but it seems like it is no longer loading the all properties page.

I'm still having trouble with this property.  I have set it as you suggested, and I am not getting any visual representation of it on the screen.  It only shows the field name and then it is blank next to it.  I think it would be really good to have Epi develop the ability to have a collection of strings for commerce as I would imagine many people would want to utilize something like that.

It seems like support was added for this based on the release notes, but I am trying to save data to the field in question via the content repostiory function.  It saves other data, but anything that is of type ItemCollection<string> is not being saved to the database even though I know I am adding it to the object.

//product exists already, update the data
                        ProductNode prod = _contentRepo.Service.Get<ProductNode>(_referenceConverter.Service.GetContentLink("Item_" + product.ItemNumber));
                        prod = prod.CreateWritableClone<ProductNode>();

                        //loop through same product and apply all state codes at once
                        if (!prod.StateRestrictions.Contains(product.StateCode))
                        {
                            prod.StateRestrictions.Add(product.StateCode);
                            _contentRepo.Service.Save(prod, SaveAction.Save);
                        }

                    

I was able to get this to start saving data.  The issue was that when using the ItemCollection<string> you have to set the value to a predefined value in the dictionary for that field.  I needed to go into commerce and manually add any values that I needed to assign programatically and then everything worked.  The next thing I need to do is programatically add those values as well so I don't have to manual do it since I have several lists to process.