\input regression-test.tex
\documentclass{article}
\usepackage{amsthm}
\usepackage{osgstyler}

\newtheorem{theorem}{Theorem}

\DeclareOsgBlockInstance{theorem}{rule-thickness=.4pt, padding=.5em}
\BindOsgBlockEnvironment{theorem}{theorem}

\UseOsgStandardBlockEnvironments
\StyleOsgBlockInstance{quote}{traits={osl-modern-rules}}
\StyleOsgBlockInstance{theorem}{traits={osl-modern-rules}}

\begin{document}
\UseOsgColorPalette{osl-modern}
\START
\ExplSyntaxOn
\__osgstyler_block_instance_resolve:n { traits={osl-modern-rules} }
\TYPE{resolved-keys=\tl_use:N\l__osgstyler_block_instance_keys_tl}
\ExplSyntaxOff
\begin{quote}
  \TYPE{quote-body=shown}
\end{quote}
\begin{theorem}
  \TYPE{theorem-body=shown}
\end{theorem}
\TYPE{done}
\END
\end{document}