%\hyphenpenalty=-1000
%\exhyphenpenalty=-1000

\vbox{\hsize=100pt
\hrule width\hsize
\noindent....................................\par
\noindent............................... \discretionary{A}{B}{CCCCCC}\par
\noindent............................ . \discretionary{AAAAAA}{BBBBBBBBB}{C} z z z\par
\noindent............................ . C z z z\par
}
\end