add option to disable uppercase locally/globally and insert hint to a…

…void issues as described in #460

examples/DEMO-TUDaBeamer2023-en.tex

@@ -116,6 +116,18 @@ \section{Slide examples}
 An example.
 \end{frame}
 
+\begin{frame}[fragile,uppercase=false]{Please be aware of uppercase frametitles}
+The mechanism to provide uppercase frame titles might have strange side effects.
+It's aware of macros, so those usually should work, but there are issues with arguments. e.g. using \verb+\color{dark2}+ will throw an error message.
+
+You can avoic this by either locally disabling the case change:
+
+\begin{verbatim}
+\frameztitle{Test \NoCaseChange{\textcolor{dark2}{\MakeUppercase{Test}}}}
+\end{verbatim}
+or use the frame option \verb+uppercase=false+ as for this frame or the class option \verb+uppercase-frametitle=false+
+\end{frame}
+
 \textcolor{TUDa-dark1}{test}
 
 \begin{frame}{Color Scheme}

tex/beamerouterthemeTUDa.sty

@@ -53,6 +53,9 @@
 	headsepline .code:n = \msg_warning:nnn {tudabeamer} {option-removed} {headsepline},
 	extendedspace .bool_gset:N = \g__ptxcd_extended_space_bool,
 	headrule .bool_gset:N = \g__ptxcd_headrule_bool,
+	uppercase-frametitle .bool_gset:N = \g__ptxcd_uppercase_frametitle_bool,
+	uppercase-frametitle .default:n = true,
+	uppercase-frametitle .initial:n = true,
 }
 
 \define@key{beamerframe}{bgcolor}{
@@ -61,6 +64,12 @@
 	}
 }
 
+\define@key{beamerframe}{uppercase}{
+	\keys_set:nn {ptxcd/beamer/outer} {
+		uppercase-frametitle=#1
+	}
+}
+
 \ProcessKeyOptions[ptxcd/beamer/outer]
 
 
@@ -193,7 +202,7 @@
 	    \usebeamerfont{frametitle}%
 	    \if@tempswa\else\csname beamer@fte#1\endcsname\fi%
 	    \vphantom{Ü}
-	    \text_uppercase:n {\insertframetitle}\strut
+	    \bool_if:NT \g__ptxcd_uppercase_frametitle_bool \text_uppercase:n {\insertframetitle}\strut
 	    \par%
 	    {%
 	      \ifx\insertframesubtitle\@empty%