\ProvidesFile{letgut.cbx}[2023-01-14 v0.9.6 letgut base citation style]
\RequireCitationStyle{numeric}
\DeclareFieldFormat[bookreview]{title}{\textbf{\emph{#1}}}
\renewbibmacro*{title}{%
  \ifboolexpr{
    test {\iffieldundef{title}}
    and
    test {\iffieldundef{subtitle}}
  }
  {}
  {\printtext[title]{%
      \printfield[titlecase]{title}%
      \setunit{\subtitlepunct}}%
    \printfield[emph]{subtitle}%
    \newunit}%
  \printfield{titleaddon}}
