Events can be triggered by form elements, in the example
we assign the function \textit{validateTime()\/} as an event
handler for the Validate event of the
\textit{zeit} choice list.
\begin{lstlisting}
validate={validateTime();}
\end{lstlisting}
If the user leaves the choice field the function is invoked
and turns the ``from'' and ``until'' text fields visible
\begin{lstlisting}
this.getField("von").display = display.visible;
this.getField("bis").display = display.visible;
\end{lstlisting}
or invisible.
\begin{lstlisting}
this.getField("von").display = display.hidden;
this.getField("bis").display = display.hidden;
\end{lstlisting}
\lstinputlisting{../examples/ex0010.tex}