Some notes on writing settings

Be careful not to overconstrain parameters

IMO Synopses currently mis-use constraints in many places

our Str multi join ( Str $separator = '', *@values )   # WRONG!

Consider:

my @y = <a b c>;
my $x = join(1, @y);

Correct is:

our Str multi join( $separator = '', *@values )        # RIGHT!