Substitute with regex conditional doesn't work

[alikve]

I tried the code from an example on https://cadabra.science/notebooks/ref_patterns.html:

Cadabra 2.3.6 (build 1.636a232 dated 2021-01-03)
Copyright (C) 2001-2020  Kasper Peeters <kasper.peeters@phi-sci.com>
Using SymPy version 1.7.1
Info at https://cadabra.science/
Available under the terms of the GNU General Public License v3

> ex:= A + B3 + C7;
A + B3 + C7
> substitute(_, $A + M? + N? | \regex{M?}{"[A-Z]7"} -> \sin(M? N?)/N?$);
  File "<console>", line 1
    substitute(_, Ex(r"A + M? + N? | \regex{M?}{"[A-Z]7"} -> \sin(M? N?)/N?", False));
                                                      ^
SyntaxError: invalid syntax
>

I use Slackware 14.2 (Python 3.7.2). I also fired up an Ubuntu 20.04.1 VPS (Python 3.8.5) and installed https://cadabra.science/packages/ubuntu2004/cadabra2-2.3.6.3-focal.deb

The result is similar:

Cadabra 2.3.6 (build 2680.636a232b66 dated 2021-01-03)
Copyright (C) 2001-2020  Kasper Peeters <kasper.peeters@phi-sci.com>
Using SymPy version 1.5.1
Info at https://cadabra.science/
Available under the terms of the GNU General Public License v3

> ex:= A + B3 + C7;
A + B3 + C7
> substitute(_, $A + M? + N? | \regex{M?}{"[A-Z]7"} -> \sin(M? N?)/N?$);
Traceback (most recent call last):
  File "/usr/lib/python3.8/code.py", line 63, in runsource
    code = self.compile(source, filename, symbol)
  File "/usr/lib/python3.8/codeop.py", line 176, in __call__
    return _maybe_compile(self.compiler, source, filename, symbol)
  File "/usr/lib/python3.8/codeop.py", line 104, in _maybe_compile
    raise err1
  File "/usr/lib/python3.8/codeop.py", line 91, in _maybe_compile
    code1 = compiler(source + "\n", filename, symbol)
  File "/usr/lib/python3.8/codeop.py", line 141, in __call__
    codeob = compile(source, filename, symbol, self.flags, 1)
  File "<console>", line 1
    substitute(_, Ex(r"A + M? + N? | \regex{M?}{"[A-Z]7"} -> \sin(M? N?)/N?", False));
                                                      ^
SyntaxError: invalid syntax
>