on Topic

[fearcadi]

I just want to be sure I understand correctly :

In your article at perl.com you describes various ways and situations
when perl creates a topic and this is described as perl making the
following binding on my behalf: 

$_ := $some_var ;  *1*

and probably marking $_ with some additional properties (e.g.  is
read-only ...) .

questions: 

???

if I will write that explicitly myself will that have *the same*
effect ?  in other words, is *1* _all_ that topic is about ?  Or there
is some additional magic. particularly , will "when" work as before ,
What will happen if I will _override_ $_ explicitly inside
e.g. "given" construct or other topicalizers:

my $x,$z;
given $x->$y {
        $_ := $z ; 
        when 2 { ... } #checks against $z ???
}


???

methods topicalize their invocant. Is $self aliased to $_ inside the
method in this ex. ?

    method sub_ether ($self: $message) {
        .transmit( .encode($message) );
    }

will it be an error to write 
    method sub_ether ($self: $message, $x is topic) {...} 

what happens if I write 
    method sub_ether ($self: $message) {
        $_ := $message ; 
        }        
or 

method sub_ether ($self: $message) {
        $_ = $message ; 
 }       

is $_ always lexical variable. Or I can have $MyPackage::_ ?


and just on the related topic :

* can I alias $something to $_ ? 
  $something := $_ 

(it seems that I can , because $_ is just another variable ) 

also , is this valid  ? 

$b := $a ; 
$c := $b ; 

( now changing value of one variable will change other two ??? )


or e.g. 

$a = 1 ; 
$Z = 10 ;

$b := $a ; 
$c := $b ; 

print $c # prints 1 
$a := $Z ; 
print $c # prints 10
$a = 5; 
print $Z # prints 5 

am I wrong ?

also 

@a :=  ( $a, $b) 
$b := $c 
@a[1] = 10 ; 
print $c # prints 10 

???

thanks 
Arcadi