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

\DeclareOsgColorPalette{block-titled-test}{
  primary = {model=HTML, value=204070},
  structure = {alias=primary},
  text = {model=HTML, value=111111},
  background = {model=HTML, value=FFFFFF}
}

\DeclareOsgBlockInstance{tb}{traits={titlebar}}
\NewOsgStyledEnvironment{tb}{tb}{none}[1]{#1}

\DeclareOsgBlockInstance{pl}{traits={framed}}
\NewOsgStyledEnvironment{pl}{pl}{none}[1]{#1}

\ExplSyntaxOn
\newenvironment{bodymodeprobe}
  {\ifvmode\TYPE{titled-list-start:passed}\else
     \TYPE{titled-list-start:FAILED}\fi
   \ifdim\parskip=0pt
     \TYPE{titled-list-parskip:passed}\else
     \TYPE{titled-list-parskip:FAILED}\fi
   \ifdim\l__osgstyler_block_body_padding_top_dim=1pt
     \TYPE{body-padding-top:passed}\else\TYPE{body-padding-top:FAILED}\fi
   \ifdim\l__osgstyler_block_body_padding_right_dim=2pt
     \TYPE{body-padding-right:passed}\else\TYPE{body-padding-right:FAILED}\fi
   \ifdim\l__osgstyler_block_body_padding_bottom_dim=3pt
     \TYPE{body-padding-bottom:passed}\else\TYPE{body-padding-bottom:FAILED}\fi
   \ifdim\l__osgstyler_block_body_padding_left_dim=4pt
     \TYPE{body-padding-left:passed}\else\TYPE{body-padding-left:FAILED}\fi
   \begin{itemize}}
  {\end{itemize}}
\ExplSyntaxOff

\begin{document}
\UseOsgColorPalette{block-titled-test}
\setlength\parskip{0pt}
\START
\ExplSyntaxOn

% 1. The titlebar trait resolves to layout=titled and is recorded.
\OsgIfBlockTitledTF { tb }
  { \TYPE { tb-titled:passed } } { \TYPE { tb-titled:FAILED } }
\OsgIfBlockTitledTF { pl }
  { \TYPE { pl-titled:FAILED } } { \TYPE { pl-titled:passed } }

% 2. An additive restyle that does not mention the layout keeps the record.
\StyleOsgBlockInstance { tb } { head-padding = 0.6em }
\OsgIfBlockTitledTF { tb }
  { \TYPE { tb-still-titled:passed } } { \TYPE { tb-still-titled:FAILED } }

% 3. An explicit layout=plain clears it.
\StyleOsgBlockInstance { tb } { layout = plain }
\OsgIfBlockTitledTF { tb }
  { \TYPE { tb-cleared:FAILED } } { \TYPE { tb-cleared:passed } }
\StyleOsgBlockInstance { tb } { traits = { titlebar } }
\StyleOsgBlockInstance { tb }
  {
    body-padding = 9pt,
    body-padding-top = 1pt, body-padding-right = 2pt,
    body-padding-bottom = 3pt, body-padding-left = 4pt
  }

\ExplSyntaxOff

% 4. Both layouts typeset without error.
\begin{tb}{Titled block}
  Body of the titled block.
\end{tb}
\begin{tb}{List block}
  \begin{bodymodeprobe}
    \item A list must not be preceded by an empty paragraph.
  \end{bodymodeprobe}
\end{tb}
\begin{pl}{Framed block}
  Body of the framed block.
\end{pl}
\TYPE{rendered:passed}
\END
\end{document}