upgrading.dbk: improve wording around transitional dummy packages

Closes: #901193
Thanks: Justin B Rye, Vincent McIntyre and Ben Hutchings

en/upgrading.dbk

@@ -1312,24 +1312,25 @@ $ aptitude purge '~c'
   </para>
 
   <section id="dummy">
-    <title>Dummy packages</title>
-    <para>
-      Some packages from &oldreleasename; have been split into several packages in &releasename;, often
-      to improve system maintainability.  To ease the upgrade path in such cases,
-      &releasename; often provides <quote>dummy</quote> packages: empty packages that have the same name as
-      the old package in &oldreleasename; with dependencies that cause the new packages to be
-      installed.  These <quote>dummy</quote> packages are considered redundant after the
-      upgrade and can be safely removed.
-    </para>
-    <para>
-      Most (but not all) dummy packages' descriptions indicate their purpose.
-      Package descriptions for dummy packages are not uniform, however, so you might
-      also find <command>deborphan</command> with the
+    <title>Transitional dummy packages</title>
+    <para>
+      Some packages from &oldreleasename; may have been replaced in &releasename;
+      by transitional dummy packages, which are empty placeholders designed to
+      simplify upgrades. If for instance an application that was formerly a single
+      package has been split into several, a transitional package may be provided
+      with the same name as the old package and with appropriate dependencies to
+      cause the new ones to be installed. After this has happened the redundant
+      dummy package can be safely removed.
+    </para>
+    <para>
+      The package descriptions for transitional dummy packages usually indicate
+      their purpose. However, they are not uniform; in particular, some
+      <quote>dummy</quote> packages are designed to be kept installed, in order
+      to pull in a full software suite, or track the current latest version of
+      some program. You might also find <command>deborphan</command> with the
       <literal>--guess-<replaceable>*</replaceable></literal> options (e.g.
-      <literal>--guess-dummy</literal>) useful to detect them in your system.  Note
-      that some dummy packages are not intended to be removed after an upgrade but
-      are, instead, used to keep track of the current available version of a program
-      over time.
+      <literal>--guess-dummy</literal>) useful to detect transitional dummy
+      packages on your system.
     </para>
   </section>