first edit

XLIMS.MVVM/Converters/CompositeCollectionConverter.cs

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+using System;
+using System.Collections;
+using System.Windows.Data;
+
+namespace XLIMS.MVVM.Converters
+{
+     [ValueConversion(typeof(object),typeof(CompositeCollection))]
+    public class CompositeCollectionConverter : IMultiValueConverter
+    {
+
+        public object Convert(object[] values
+            , Type targetType
+            , object parameter
+            , System.Globalization.CultureInfo culture)
+        {
+            var res = new CompositeCollection();
+            foreach (var item in values)
+                if (item is IEnumerable)
+                    res.Add(new CollectionContainer()
+                    {
+                        Collection = item as IEnumerable
+                    });
+                else res.Add(item);
+            return res;
+        }
+
+        public object[] ConvertBack(object value
+            , Type[] targetTypes
+            , object parameter
+            , System.Globalization.CultureInfo culture)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}