Adjust rest position in drum parts?

[Charles Marshall]

How can I position rests vertically within a DrumVoice in a simple way?  There are conflicts with rests in other DrumVoices.  The use of \rest as within a Voice doesn't work for me; it gives

 error: unrecognized string, not in text script or \lyricmode cymr4 sn8
                                                                                                            a8\rest ....
Charlie

PS.  I looked a long time but couldn't find it in the docs or on line.