I suppose a parish priest might give a few verbal pointers to the organist. Play here, don't play here, that sort of thing. Fr Adrian Fortescue went a little bit further.
The Liber Organi is an incredibly beautiful hand-written book which Fortescue wrote to provide the organist at his church, St Hugh’s in Letchworth, with everything needed to accompany the liturgies. The inside front cover contains a photograph of the church taken in 1916 and the inside back cover contains the author's dedication 'in perpetuity' to St Hugh's.