%%
%% The LaTeX Companion, 3ed
%%
%% Example A-3-14 on page II-666 in "Paragraph boxes".
%%
%% 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{183.0pt}
%StartShownPreambleCommands
\usepackage{calc}
%StopShownPreambleCommands

\begin{document}
xx \fbox{\parbox[b][\height+\baselineskip][s]
                {20mm}
                {Some text on top. \par\vfill
                 And a few lines on the
                 bottom of the box.}}
   \fbox{\parbox[b][\height+\baselineskip][s]
                {20mm}
                {This time a few lines on the
                 top of the box. But only one
                 line \par\vfill down here.}} xx
\end{document}