\def\typeout{\immediate\write17} \newcount\CNT\newcount\CNTs \def\TEST#1#2#3{\par$#1{xyz}#2\CNT=\lastnodetype\CNTs=\lastnodesubtype\typeout{\string #1: (\the\CNT,\the\CNTs)}#3$} \TEST\displaystyle\displaystyle{} \TEST\textstyle\textstyle{} \TEST\mathchoice{{a}{a}{a}}{} \TEST\mathord{}{} \TEST\mathop\displaylimits{} \TEST\mathop\limits{} \TEST\mathop\nolimits{} \TEST\mathbin{}{} \TEST\mathrel{}{} \TEST\mathopen{}{} \TEST\mathclose{}{} \TEST\mathpunct{}{} \TEST\mathinner{}{} \TEST\sqrt{}{}% radical \TEST\underline{}{} \TEST\overline{}{} \TEST\vcenter{}{} \TEST\dot{}{}% accent \TEST{left}{\left[}{\right]} \TEST{middle}{\left(\middle|}{\right)} \TEST{\left[\right]}{}{} % TODO: right, fraction \bye