Is there a way to add alphabetical ordered list

Hey, @artf thanks for creating this awesome library. its really helpful. I am using it in angular and I have used order list with numbers but it would be really helpful if there is a way to add an alphabetical ordered list or in roman numbers I was trying this

this._editor.RichTextEditor.add('orderedList',
          {
            icon: 'a',
            attributes: { title: 'Ordered List',type:'a' },
            result: rte => rte.exec('insertOrderedList'),

          });

but didn't work. please help