MarkupBlock - [0..12)::12 - [<!-- foo -->]
    MarkupCommentBlock - [0..12)::12
        MarkupTextLiteral - [0..4)::4 - [<!--] - Gen<Markup> - SpanEditHandler;Accepts:None
            OpenAngle;[<];
            Bang;[!];
            DoubleHyphen;[--];
        MarkupTextLiteral - [4..9)::5 - [ foo ] - Gen<Markup> - SpanEditHandler;Accepts:Whitespace
            Whitespace;[ ];
            Text;[foo];
            Whitespace;[ ];
        MarkupTextLiteral - [9..12)::3 - [-->] - Gen<Markup> - SpanEditHandler;Accepts:None
            DoubleHyphen;[--];
            CloseAngle;[>];
