What is attributes (sub :lvalue, etc

Attributes in Perl are special annotations that can be applied to packages, variables, subroutines, and other constructs to modify their behavior. The `:lvalue` attribute is one of these attributes, indicating that a subroutine can be used in a context where it's expected to return a modifiable value. This allows you to use the subroutine as if it were a variable.

Here’s an example of a subroutine with the `:lvalue` attribute:


    sub foo :lvalue {
        return $value;
    }
    
    my $value = 10;
    foo = 20;  # modifies the value returned by foo
    print $value;  # prints 20