Edge labels

You can write edge labels. They should be specified as the optional argument of \chunk. Note that the width of an edge label is neglected. If you write

\begin{bundle}{xxx}
\chunk[left]{aaa}
\chunk{
        \begin{bundle}{yyy}
        \chunk{bbb}
        \chunk{ddd}
        \end{bundle}}
\chunk[right]{ccc}
\end{bundle}