fix setting element props using an element derived value

Author: Angel-foxxo

AttributeList.cs

@@ -273,8 +273,8 @@ public virtual object? this[string name]
                         {
                             var valueType = value.GetType();
 
-                            // type must be equal, or a superclass
-                            if (prop.PropertyType != valueType && valueType.IsSubclassOf(prop.PropertyType))
+                            // types must be equal, or a superclass
+                            if (prop.PropertyType != typeof(Element) && valueType.IsSubclassOf(prop.PropertyType))
                             {
                                 throw new InvalidDataException($"class property '{prop.Name}' with type '{prop.PropertyType}' does not match the type '{valueType}' of the value being set, this is likely a mismatch between the real class and the class from the datamodel");
                             }

Tests/ValveMap.cs

@@ -180,7 +180,7 @@ internal class CMapSelectionSet : DMElement
 {
     public Datamodel.ElementArray Children { get; } = [];
     public string SelectionSetName { get; set; } = string.Empty;
-    public CObjectSelectionSetDataElement SelectionSetData { get; set; } = [];
+    public DMElement SelectionSetData { get; set; } = [];
 
     public CMapSelectionSet() { }
     public CMapSelectionSet(string name)
@@ -195,6 +195,12 @@ internal class CObjectSelectionSetDataElement : DMElement
     public Datamodel.ElementArray selectedObjects { get; set; } = [];
 }
 
+internal class CFaceSelectionSetDataElement : DMElement
+{
+    public Datamodel.IntArray faces { get; set; } = [];
+    public Datamodel.ElementArray meshes { get; set; } = [];
+}
+
 
 internal class CMapEntity : BaseEntity
 {