C++ {\it bitwise-or} operator. For example:
\begin{verbatim}
- wxCAPTION | wxMINIMIZE_BOX | wxMINIMIZE_BOX | wxTHICK_FRAME
+ wxCAPTION | wxMINIMIZE_BOX | wxMAXIMIZE_BOX | wxTHICK_FRAME
\end{verbatim}
For the window styles specific to each window class, please see the documentation