SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://www.progress.com/documentation/sitefinity-cms/edit-properties-values-displayed-inside-the-property-editor-mvc

ExpandableObjectConverter.cs

using System.ComponentModel;

public partial class TypeConverterSnippets
{
    [TypeConverter(typeof(ExpandableObjectConverter))]
    public MyClass MyClass
    {
        get => this.model;
    }

    private MyClass model = new MyClass();
}

public class MyClass { }

It is incredibly unclear what this code is intended to accomplish.