-L<LaTeX::TikZ::Set> objects that are mutable consume this role.
-This forces them to implement an C<add> method describing how more elements can be added to the set.
+L<LaTeX::TikZ::Set> objects that group other objects together consume this role.
+This forces them to implement :
+
+=over 4
+
+=item *
+
+a C<kids> method that returns the list of subobjects ;
+
+=item *
+
+an C<add> method describing how more elements can be added to the set.
+
+=back