Controlling vertical space in embedded tabu environment

Question

When using embedded tabu environments I have difficulties having different vertical space in the outer and inner tables. Consider these simple embedded tabu tables:

\documentclass[a4paper]{article}
\usepackage{tabu}

\begin{document}
  \begin{tabu}{|c|}
    \hline
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
  \end{tabu}
\end{document}

The table renders like this:

As you can see, the large text is too close to the upper \hline. To fix this I try to use the \tabulinesep command before the first/outer table:

(I use a large 5pt spacing to make it obvious what happens.)

\documentclass[a4paper]{article}
\usepackage{tabu}

\begin{document}
  \tabulinesep=^5pt % <==== At least 5pt above text.
  \begin{tabu}{|c|}
    \hline
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
  \end{tabu}
\end{document}

However, it leaves gaps above the vertical rules (lines) as the \tabulinesep also applies to the outer table:

To fix it, I can use a \tabulinesep command right above the two innner tables where it should apply like this:

\documentclass[a4paper]{article}
\usepackage{tabu}

\begin{document}
  \begin{tabu}{|c|}
    \hline
    \tabulinesep=^5pt % <==== At least 5pt above text in inner table.
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
    \tabulinesep=^5pt % <==== At least 5pt above text in inner table.
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
  \end{tabu}
\end{document}

Which renders the correct result:

However, I do not want to repeat myself for each inner table. So what I really want is to set a global default, and then make an exception for the outer table. My guess would be this but it does not work:

\documentclass[a4paper]{article}
\usepackage{tabu}

\global\tabulinesep=^5pt % <=== Global setting

\begin{document}
  \tabulinesep=^0pt % <==== Cannot override for outer table only... :-(
  \begin{tabu}{|c|}
    \hline
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
    \begin{tabu}{l|c|r}
      left & {\LARGE \textbf{MIDDLE}} & right
    \end{tabu} \\
    \hline
  \end{tabu}
\end{document}

The result is the first image (where I started out).

Any suggestions for setting a global \tabusep and then override it for the outer table?

Answer 1

You can insert a strut, just for its height part in case only uppercase is used. I show both examples.

\documentclass[a4paper]{article}
\usepackage{amsmath} % for a better \smash
\usepackage{tabu}

\begin{document}
  \begin{tabu}{|c|}
    \hline
    \begin{tabu}{l|c|r}
      left & \LARGE\smash[b]{\strut}\textbf{MIDDLE} & right
    \end{tabu} \\
    \hline
    \begin{tabu}{l|c|r}
      left & \LARGE\strut\textbf{MIDDLEg} & right
    \end{tabu} \\
    \hline
  \end{tabu}
\end{document}