Markup block - Gen<None> - 9 - (0:0,0)
    Transition span - Gen<None> - [@] - SpanEditHandler;Accepts:None - (0:0,0) - Symbols:1
        HtmlSymbolType.Transition;[@];
    MetaCode span - Gen<None> - [:] - SpanEditHandler;Accepts:Any - (1:0,1) - Symbols:1
        HtmlSymbolType.Colon;[:];
    Markup span - Gen<Markup> - [foo bar] - SpanEditHandler;Accepts:Any - (2:0,2) - Symbols:3
        HtmlSymbolType.Text;[foo];
        HtmlSymbolType.WhiteSpace;[ ];
        HtmlSymbolType.Text;[bar];
