This is the base class from which PopMenuItem objects derive.

Autodesk.AutoCAD.Customization.ElementBase
    Autodesk.AutoCAD.Customization.VersionableElement
        Autodesk.AutoCAD.Customization.CustomizationElement
            Autodesk.AutoCAD.Customization.PopMenuItemBase
                Autodesk.AutoCAD.Customization.PopMenuItem
                Autodesk.AutoCAD.Customization.PopMenuRef

Public abstract Class PopMenuItemBase
Inherits CustomizationElement

public abstract class PopMenuItemBase : CustomizationElement;