[tex-eplain] btxmac.tex causes Runaway definition and Forbidden control sequence on compile.

[terry.s at Safe-mail.net]

Hello,

I have TeX Live 2022 installed on Windows 10, and am learning TeX and eplain.
If I try to compile a (previously fine) document with 'btxmac.tex' loaded, I get a "Runaway definition" error.
I believe the problem is in the source of 'btxmac.tex' for 3 reasons:

1) It compiles fine without it.
2) The error references macros I don't have in my document (including some with '@' and '@@').
3) The error references "L. 357" but my source barely tops 200 lines. (The example attached only has 18.)

Below are error and *minimal example* source (which I will also attach):

**Error**
This is TeX, Version 3.141592653 (TeX Live 2022) (preloaded format=tex)
(./eplain-01.tex (c:/texlive/2022/texmf-dist/tex/eplain/eplain.tex)
(c:/texlive/2022/texmf-dist/tex/eplain/btxmac.tex
Runaway definition?
[#1]->\def \@optionalarg {#1}\let 
! Forbidden control sequence found while scanning definition of \@@getoptionala
rg.
<inserted text> 
                }
<to be read again> 
                   \@optdummy 
l.357    \let\@optdummy
                       =\relax % just in case it has become \outer somehow
? 

**Example TeX Code**
\input eplain
\input btxmac.tex
\beginpackages
\usepackage{url}
\endpackages
\enablehyperlinks
\parskip=\baselineskip
% SHORTCUTS + CUSTOM DEFINITIONS (retained in case they contribute to error):
\def\footnote{\numberedfootnote}
\def\bslash{$\backslash$}
\def\mycmd #1{{\tt\bslash#1}}
\def\startnoskip{\bgroup\parskip=0pt}
\def\endnoskip{\egroup}
\def\mysep{\vskip2pt\centerline{$ˆ{\vrule width2cm height .5pt}$}\vskip2pt\noindent}

\beginsection Minimal Example (with eplain, btxmac.tex and url)
Hello there!
\bye
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