IEnumerable interface definition

Question

I took a look at the definition of the IEnumerable interface

public interface IEnumerable
    {
        // Summary:
        //     Returns an enumerator that iterates through a collection.
        //
        // Returns:
        //     An System.Collections.IEnumerator object that can be used to iterate through
        //     the collection.
        [DispId(-4)]
        IEnumerator GetEnumerator();
    }

I don't understand what is this attribute [DispId(-4)] and why its value is equal to -4 ?

Thanks,