src/HOL/SPARK/Manual/document/root.bib

drop pointless print_mode operations Output.output / Output.escape;

@Book{Barnes,
  author =       {John Barnes},
  title =        {{T}he \textsc{Spark} {A}pproach to {S}afety and
                  {S}ecurity},
  publisher =    {Addison-Wesley},
  year =         2006
}