[Parameter] elaborate on parcel and capture params, raiph++

Author: moritz

lib/Parameter.pod

@@ -45,14 +45,26 @@ Returns C<True> for optional parameters.
 
 Returns C<True> for parcel parameters.
 
-    sub f(\$parcel, $non-parcel) { }
+    sub f(\$parcel) {
+        $parcel = 5;
+    }
+    f(my $x);   # works
+    f(42);      # dies in the assignment
+
+Parcel parameters bind either a variable or a value passed to it, with
+no decontainerization happen.  That means that if a variable was passed
+to it, you can assign to the parameter. This is different from
+L<rw|#rw>-parameter which can only bind to variables, never to values.
 
 =head2 capture
 
 Returns C<True> for parameters that capture the rest of the argument list.
 
     sub f(\capture) { }
 
+Capture parameters do not force any context on the values passed bound
+to them, which is why they cannot have sigils.
+
 =head2 rw
 
 Returns C<True> for C<is rw> parameters.