\ProvidesFile{letgut.cbx}[2022-03-22 v0.9.1 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}}