I built up a simple UML diagram, where one of the class boxes has an union containing a number of elements. I want to show that those elements are part of an union.

But how can I do so with tikz? I tried to use a matrix, but it complains that I cannot nest matrices.

```
\documentclass[a4paper,12pt]{scrreprt}
\usepackage[utf8x]{inputenc}
\usepackage{tikz}
\usetikzlibrary{matrix,positioning,calc,arrows,shapes}
\tikzstyle{class}=[matrix of nodes, draw=black, font=\ttfamily\small]
\begin{document}
\begin{tikzpicture}[node distance=2cm]
\matrix (value) [class] {
\textbf{Value} \\
\hline
TypeA m\_type \\
\textit{Union:} \\ % TODO: want to have a rectangle around the next 6 entries!
TypeB int64Val\\
TypeC float64Val\\
TypeD stringVal\\
TypeE *funcVal\\
TypeF varsVal\\
};
\end{tikzpicture}
\end{document}
```

## Best Answer

The first coordinate in the draw statement is the projection of

`(value-3-1.north west)`

(top left anchor the the first node in the third row) to the line between`(value.north west)`

and`(value.south west)`

and then shifting 4pt to the right.