[Signature] parameter traits and modifiers

lib/Signature.pod

@@ -130,6 +130,34 @@ notionally) computed anew for each call
     :($goal, $accuarcy = $goal / 100);
     :(:$excludes = ['.', '..']);        # a new Array for every call
 
+=head2 Parameter Traits and Modifiers
+
+By default, parameters are bound to their argument and marked as
+read-only. One can change that with traits on the parameter.
+
+The C<is copy> trait causes the argument to be copied, and allows it
+to be modified inside the routine
+
+    sub c($x is copy) {
+        $x = Inf if $x ~~ Whatever;
+        .say for 1..$x;
+    }
+
+The C<is rw> trait makes the parameter only bind to a variable (or other
+writable container)N<this does not work yet in Rakudo>. Assigning to the
+parameter changes the value of the variable at the caller side
+
+    sub swap($x is rw, $y is rw) {
+        ($x, $y) = ($y, $x);
+    }
+
+To bind either to a value or a variable, one can prefix a parameter with
+a backslash C<\>.
+
+    sub f(\$raw) { ... }
+
+Prefixing a parameter with a vertical bar C<|> makes it use up all the
+remaining positional and named arguments.
 
 =head1 Methods