Forgot to put parentheses around the rule numbers for cprulecustnum.

README.txt

@@ -30,7 +30,6 @@
 %%Constructive pull requests, creation of issues for bugs, and suggestions for improvements are very welcome.
 %%
 %%This package was originally created to assist me while writing a paper on cP systems which should also largely re-appear in my PhD dissertation.  While you are certainly free to peruse and use this package, if you don't know what Membrane Computing/P systems is, this package is unlikely to be of much use to you.
- % Also be aware that some of the commands included in the package aren't currently documented outside of section \ref{sec:implementation}.  The commands exist and are used, but I haven't had the spare time to write about them properly yet.
 \endinput
 %%
 %% End of file `README.txt'.

cpsystems.dtx

@@ -104,7 +104,7 @@
 % 
 % Note that, at present, this package is \emph{not} available on CTAN, and instead may only be retrieved from the author's academic GitHub account (see the URL listed in this document's title).  Once it has been sufficiently developed and stabilised, and/or there is consistent demand for such a package beyond the author's immediate research group, it likely will be added to CTAN, but there is no timeframe nor guarantee in place for that.
 %
- % Also be aware that some of the commands included in the package aren't currently documented outside of section \ref{sec:implementation}.  The commands exist and are used, but I haven't had the spare time to write about them properly yet.
+% Also be aware that some of the commands included in the package aren't currently documented outside of section \ref{sec:implementation}.  The commands exist and are used, but I haven't had the spare time to write about them properly yet.
 %
 % \section{Usage}
 %
@@ -642,7 +642,7 @@
 % 	Mostly the same as a regular |\cprule|, but takes the rule number to display as an extra parameter.  This also does \emph{not} increment the rule counter.  I'm yet to work out how you could make references to these rule numbers.  This is currently basically just a quick hack to permit the display of alternatives of pre-existing rules, and right now everything must be updated manually.
 %    \begin{macrocode}
 \newcommand*{\cprulecustnum}[6]{
-	\cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{#6}
+	\cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{(#6)}
 }
 %    \end{macrocode}
 % \end{macro}

cpsystems.sty

@@ -22,7 +22,6 @@
 \ProvidesPackage{cpsystems}
 [2021/07/14 v0.18 Package to aid in typesetting cP systems
 rulesets, following Nicolescu's standard style]
- % Also be aware that some of the commands included in the package aren't currently documented outside of section \ref{sec:implementation}.  The commands exist and are used, but I haven't had the spare time to write about them properly yet.
 
 \RequirePackage{array}
 \RequirePackage{framed}
@@ -59,7 +58,7 @@ rulesets, following Nicolescu's standard style]
 \cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{}
 }
 \newcommand*{\cprulecustnum}[6]{
-\cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{#6}
+\cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{(#6)}
 }
 \newcommand*{\cppromoter}[1]{
 \cpsystems@cpprominhi{|}{#1}