Trying to learn/use subroutine attributes. However, can't seem to take very first steps :(

Following example code, gives an error:

Invalid CODE attribute: hold at ./attr.pl line 6

What am I doing wrong?

Thanks for you help.

where attr.pl is :

-----------------------------
#!/usr/bin/perl
package XYZ;
use strict;

sub abc :hold
{
}

sub MODIFY_CODE_ATTRIBUTES
{
    my ($pack,$ref,$attrs) = @_;
    ();
}

sub FETCH_CODE_ATTRIBUTES
{
    return ('hold');
}


1;
__END__
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