%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-7-13 on page II-202 in "Ghostbusters\texttrademark ".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{57.0pt}

%StartShownPreambleCommands
\usepackage{color,mathtools} \setlength\fboxrule{0pt}\setlength\fboxsep{0pt}
\newcommand\xx[2]{{\scriptscriptstyle #1}\boxed{#2\color{blue}\vrule}\,}
%StopShownPreambleCommands

\begin{document}
$ (a) \xx{1}{\mathstrut}         % normal strut (size of parentheses)
 \xx{2}{\xmathstrut{0}}          % 0 gives normal strut
 \xx{3}{\xmathstrut{0.5}}        % add 50% at top + bottom (= 100% bigger)
 \xx{4}{\xmathstrut[0]{-0.2}}    % remove 20% from top, but keep bottom
 \xx{5}{\xmathstrut[0.3]{-1}}    % bottom 30% larger, no height
 \xx{6}{\xmathstrut{-0.5}} (z) $ % -> see explanation below ...
\end{document}