'+' . sub { ... }
    '+' . \&subname
    '+' . [\&subname]
    '+' . [\&subname, @args]
    ['+' . \&subname]
    ['+' . \&subname, @args]
    '+' . $coderef
    '+' . [$coderef]
    '+' . [$coderef, @args]
    ['+' . $coderef]
    ['+' . $coderef, @args]

##</code><code>##

... '+' . Tkx::i::interp->create_tcl_sub( CODEREF ) ...

##</code><code>##

my $interp = Tkx::i::interp();
... '+' . $interp->create_tcl_sub( CODEREF ) ...

##</code><code>##

sub { ... }
\&subname
$coderef

##</code><code>##

Error: invalid command name "::perl::CODE(0x7ffef5dd34d8)"