I coded a really simple test class that would handle the "DEFINITION" subroutine attribute and would just print whatever it got. Just for testing.

package Class::Definition;

use Attribute::Handlers;

sub UNIVERSAL::DEFINITION : ATTR(CODE) {
    print "UNIVERSAL::DEFINITION: @_\n";
}

1;
[download]

That's all sweet and dandy and if I say:

use Class::Definition;

sub TEST : DEFINITION('whatever') {}
[download]

I succesfully get this printed: UNIVERSAL::DEFINITION: main GLOB(0x283179c) CODE(0x225454) DEFINITION whatever CHECK

Now comes the tricky part.
I think the code below should work. But it doesn't. I don't know if there's an obvious mistake and I'll be ashamed for eternity for ever writing this node. But I truely believe it's some kind of perl bug, but I hope to be wrong. Here's the code:

use warnings;
use strict;
use Class::Definition;

sub CLASS : DEFINITION(

    ATTRIBUTES:
        PRIVATE:    pvt_at1 pvt_at2 pvt_at3
        PROTECTED:  ptc_at1 ptc_at2 ptc_at3
        PUBLIC:     pub_at1 pub_at2 pub_at3
    
    METHODS:
        PRIVATE:    pvt_mt1 pvt_mt2 pvt_mt3
        PROTECTED:  ptc_mt1 ptc_mt2 ptc_mt3
        PUBLIC:     pub_mt1 pub_mt2 pub_mt3

);
[download]

When it runs I get this error message:

Invalid CODE attribute:   pub_mt1 (

        ATTRIBUTES:
                PRIVATE:    pvt_at1 pvt_at2 pvt_at3
                PROTECTED:  ptc_at1 ptc_at2 ptc_at3
                PUBLIC:     pub_at1 pub_at2 pub_at3

        METHODS:
                PRIVATE:    pvt_mt1 pvt_mt2 pvt_mt3
                PROTECTED:  ptc_mt1 ptc_mt2 ptc_mt3
                PUBLIC:     pub_mt1 pub_mt2 pub_mt3

) at attrtest.pl line 6
BEGIN failed--compilation aborted at attrtest.pl line 18.
[download]

Do you see something wrong there? The attribute name got changed to pub_mt1, which is a substring of the attribute parameter.
But wait, there's even more weirdness. If I strip some lines off the code, so that it ends up like this:

use warnings;
use strict;
use Class::Definition;

sub CLASS : DEFINITION(

    ATTRIBUTES:
);
[download]

I get this as an error:

Invalid CODE attribute:
 INITION(

        ATTRIBUTES:
) at attrtest.pl line 6
BEGIN failed--compilation aborted at attrtest.pl line 9.
[download]