Markup block - Gen<None> - 5 - (0:0,0)
    Tag block - Gen<None> - 5 - (0:0,0)
        Markup span - Gen<Markup> - [<foo>] - SpanEditHandler;Accepts:None - (0:0,0) - Symbols:3
            HtmlSymbolType.OpenAngle;[<];
            HtmlSymbolType.Text;[foo];
            HtmlSymbolType.CloseAngle;[>];
