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\begin{tabular}{l|p{15mm}}
\hline
foo & bar \newline rlz \\
\hline
\end{tabular}
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\documentclass{article}
\begin{document}
\begin{tabular}{ccc}
one & two & three \\
one & two & \shortstack{aa \\ bb}\\
\end{tabular}
\end{document}
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\begin{tabular}{llp{5cm}}
CCCCCCCC & DDDD & \parbox{5cm}{Betty Botter Thought: \\ If I Put This Bitter Butter in My Batter it Will Make My Batter Bitter}