diff --git a/doc/environments/fancythm/Makefile b/doc/environments/fancythm/Makefile
new file mode 100644
index 0000000..fbaf459
--- /dev/null
+++ b/doc/environments/fancythm/Makefile
@@ -0,0 +1,21 @@
+sty: clean-sty
+	pdflatex fancythm.ins
+
+all: clean pdf sty
+
+pdf:
+	pdflatex fancythm.dtx
+	makeindex -s gind.ist fancythm.idx
+	pdflatex fancythm.dtx
+
+clean: clean-sty
+	latexmk -c fancythm.dtx
+	rm -f fancythm.hd
+	rm -f fancythm.glo
+	rm -f fancythm.pdf
+
+clean-sty:
+	rm -f fancythm.sty
+	rm -f fancythm.tdo
+
+.PHONY: pdf clean
diff --git a/doc/environments/fancythm/fancythm.dtx b/doc/environments/fancythm/fancythm.dtx
new file mode 100644
index 0000000..36eb978
--- /dev/null
+++ b/doc/environments/fancythm/fancythm.dtx
@@ -0,0 +1,128 @@
+% \iffalse meta-comment
+%
+%% File: fancytm.dtx
+%
+% Copyright (C) 2022 Maximilian Keßler
+%
+% It may be distributed and/or modified under the conditions of the
+% LaTeX Project Public License (LPPL), either version 1.3c of this
+% license or (at your option) any later version.  The latest version
+% of this license is in the file
+%
+%    https://www.latex-project.org/lppl.txt
+%
+% -----------------------------------------------------------------------
+%<package>\ProvidesExplPackage{fancythm}{2022/01/17}{0.0.1}{Grouped theorems.}
+%
+%<*driver>
+\documentclass[full,kernel]{l3doc}
+\usepackage{mkessler-todo}
+\begin{document}
+  \DocInput{\jobname.dtx}
+\end{document}
+%</driver>
+% \fi
+%
+% \title{^^A
+%   The \pkg{fancythm} package^^A
+% }
+%
+% \author{^^A
+%      Maximilian Keßler
+% }
+%
+% \date{Released 2022-01-12}
+%
+% \maketitle
+%
+% \begin{documentation}
+% \end{documentation}
+% 
+% 
+% \begin{implementation}
+% 
+% \section{\pkg{fancythm} implementation}
+%
+%    \begin{macrocode}
+%<*package>
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<@@=fancythm>
+%    \end{macrocode}
+%
+%
+%
+%    \begin{macrocode}
+\cs_set_eq:NN \arabic:n \arabic
+\cs_set_eq:NN \counter_new:n \newcounter
+\cs_set_eq:NN \counter_within:nn \counterwithin
+\cs_new:Npn \counter_new:nn #1 #2
+  {
+    \counter_new:n { #1 }
+    \counter_within:nn { #1 } { #2 }
+  }
+\cs_set_eq:Nc \counter_alias:nn { @counteralias } % this is from thmtools
+\cs_set_eq:Nc \counter_undefined_error:n { @nocounterr }
+
+\cs_new:Npn \counter_if_exist_p:n #1 
+  {
+    \cs_if_exist_p:c { c@ #1 }
+  }
+\cs_new:Npn \counter_if_exist:nT #1
+{
+  \cs_if_exist:cT { c@ #1 }
+}
+\cs_new:Npn \counter_if_exist:nF #1
+{
+  \cs_if_exist:cF { c@ #1 }
+}
+\cs_new:Npn \counter_if_exist:nTF #1
+{
+  \cs_if_exist:cTF { c@ #1 }
+}
+
+\cs_new:Npn \counter_ensure_exist:n #1 
+{
+  \counter_if_exist:nF { #1 }
+  {
+    \counter_undefined_error:n { #1 }
+  }
+}
+\cs_new:Npn \counter_the:n #1
+  {
+    \use:c { the #1 }
+  }
+\cs_new:Npn \counter_set_the:nn #1 #2
+  {
+    \counter_ensure_exist:n { #1 }
+    \exp_args:Nc \renewcommand { the #1 } { #2 }
+  }
+\cs_new:Npn \counter_sub:nn #1 #2
+  {
+    \counter_within:nn { #1 } { #2 }
+    \counter_set_the:nn { #1 } 
+    {
+      \counter_the:n { #2 } . \arabic:n { #1 }
+    }
+  }
+\cs_new:Npn \@@_counter_sub_if_exist:n #1
+{
+  \counter_if_exist:nT { #1 }
+  {
+    \counter_sub:nn { in #1 } { #1 }
+  }
+}
+%    \end{macrocode}
+% 
+% 
+% 
+%    \begin{macrocode}
+%</package>
+%    \end{macrocode}
+%
+%   \end{implementation}
+% 
+% 
+% 
+% \newpage
diff --git a/doc/environments/fancythm/fancythm.ins b/doc/environments/fancythm/fancythm.ins
new file mode 100644
index 0000000..2bd1bca
--- /dev/null
+++ b/doc/environments/fancythm/fancythm.ins
@@ -0,0 +1,4 @@
+\input docstrip.tex
+\keepsilent
+\generate{\file{fancythm.sty}{\from{fancythm.dtx}{package}}}
+\end