Merge pull request #3048 from gdonald/roles-is-or-does

Roles can also be mixed in using 'is'.

Author: JJ

doc/Language/objects.pod6

@@ -742,8 +742,13 @@ and code reuse within objects.
 
 X<|does>
 Roles use the keyword C<role> preceding the name of the role that is
-declared. Roles are mixed in using the C<does> keyword preceding the name
-of the role that is mixed in.
+declared. Roles are mixed in using the C<does> keyword preceding the name of
+the role that is mixed in.
+
+Roles can also be mixed into a class using C<is>. However, the semantics of
+C<is> with a role are quite different from those offered by C<does>. With C<is>,
+a class is punned from the role, and then inherited from. Thus, there is no
+flattening composition, and none of the safeties which C<does> provides.
 
 =begin code
 constant ⲧ = " " xx 4; #Just a ⲧab