better example per hackedNODE@perl6.party

doc/Type/Signature.pod6

@@ -152,9 +152,14 @@ the C<where>-clause inside the sub-signature.
 
 =head3 Constraining Optional Arguments
 
-L<Optional arguments|Optional_and_Mandatory_Parameters> can have constraints, too:
+L<Optional arguments|Optional_and_Mandatory_Parameters> can have constraints, too.
+Here we want an optional UInt parameter that, if used, must be greater than 5:
 
-    sub bin2hex($bin, Int $len where {$len >= 0} = 0) { ... }
+    sub f(Int $a, UInt $i? where { !$i.defined or $i > 5 } ) { ... }
+
+The signature may be made a bit simpler (but more obscure for the less expert eye) by using defaults:
+
+    sub f(Int $a, UInt $i? where { !.defined or $_ > 5 } ) { ... }
 
 =head3 Constraining Slurpy Arguments