Relevant to bidirectional translation applications: switches on a mode where input can be passed to either side of the bidirectional system. Commands for the question'' side are prefaced with Q:'', e.g. \begin{verbatim} Q: LOAD_TRANSLATE

Q: where is the pain \end{verbatim} while commands for the `answer'' side are prefaced with ``A:'', e.g. \begin{verbatim} A: EBL_LOAD

Q: en la cabeza \end{verbatim}