...
use 5.026;
...
use constant {
    ...
    ERR_CALLBACK_NOT_CODEREF    => 'Callback is not a coderef.',
};
...
use Scalar::Util 'reftype';
...
use Tkx;
...
{
    use constant BINDPLUS_REF_BASE => 'bindplus_ref_base_';

    my ($tcl_interp, $tcl_sub_ref_id);
    BEGIN {
        $tcl_interp = Tkx::i::interp();
        $tcl_sub_ref_id = 0;
    }

    sub bindplus {
        my ($tag, $seq, $callback) = @_;

        my $callback_ref = reftype $callback;

        if ($callback_ref eq 'CODE') {
            Tkx::bind($tag, $seq, '+' . $tcl_interp->create_tcl_sub(
                $callback, undef, undef, BINDPLUS_REF_BASE . $tcl_sub_ref_id++
            ));
        }
        elsif ($callback_ref eq 'ARRAY') {
            if (reftype $callback->[0] eq 'CODE') {
                Tkx::bind($tag, $seq, '+' . $tcl_interp->create_tcl_sub(
                    sub { $callback->[0]->($callback->@[1 .. $callback->$#*]) },
                    undef, undef, BINDPLUS_REF_BASE . $tcl_sub_ref_id++
                ));
            }
            else {
                croak ERR_CALLBACK_NOT_CODEREF;
            }
        }
        else {
            croak ERR_CALLBACK_NOT_CODEREF;
        }
    }
}

##</code><code>##

$callback, undef, undef, BINDPLUS_REF_BASE . $tcl_sub_ref_id++

##</code><code>##

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