A display equation whose cells are pictures, with blank lines inside them
(smoke-test issue #70): the blank line belongs to the nested environment, not
to the math body, so the math still pairs with its closer.

\[\arraycolsep=0.25em\def\arraystretch{2.2}
  \begin{array}{ccc}
  \displaystyle\frac{Z(m^2, \lambda)}{Z(m^2, 0)} & \sim &
  \begin{tikzpicture}[eqpic]
    \node [circ] at (0, 0) {};

    \draw (0, 0.5) ellipse (0.3 and 0.5);
    \draw (0, -0.5) ellipse (0.3 and 0.5);
  \end{tikzpicture}\\
  && 1 &+& \displaystyle\frac{-\lambda \hbar}{m^4} \frac{1}{8}
\end{array}
\]

The same holds for the other math delimiters:

$$
\begin{tikzpicture}
  \draw (0, 0) -- (1, 1);

  \draw (1, 1) -- (2, 0);
\end{tikzpicture}
$$

\(
\begin{tikzpicture}
  \node {a};

  \node {b};
\end{tikzpicture}
\)

A brace group nested in math is the same story: `math_group` consumes the
blank line as ordinary body trivia.

\[
  \text{a

  b}
\]
