The pitch to use for @code{\transposition} should correspond to
the real sound heard when a@tie{}@code{c'} written on the staff is
-played by the transposing instrument.
+played by the transposing instrument. @code{\transposition}
+should @emph{only} be used if the pitches are @emph{not} being
+entered in concert pitch.
Here are a few notes for violin and B-flat clarinet where the
parts have been entered using the notes and key as they appear in
\set Staff.midiInstrument="clarinet"
\transposition bes
+ % not concert pitch
\key d \major
a4( d8) r d r d4
}