document ButAutomaticUpgrades together with NotAutomatic

as suggested by Charles Plessy (Closes: #619083)

debian/changelog

@@ -11,8 +11,10 @@ apt (0.8.13.1) UNRELEASED; urgency=low
     - adapt to new gnumach kernel package naming (Closes: #619337)
   * doc/apt_preferences.5.xml:
     - correct typo spotted by Charles Plessy (Closes: #619088)
+    - document ButAutomaticUpgrades together with NotAutomatic
+      as suggested by Charles Plessy (Closes: #619083)
 
- -- David Kalnischkies <kalnischkies@gmail.com>  Wed, 23 Mar 2011 02:08:23 +0100
+ -- David Kalnischkies <kalnischkies@gmail.com>  Wed, 23 Mar 2011 02:19:33 +0100
 
 apt (0.8.13) unstable; urgency=low
 

doc/apt_preferences.5.xml

@@ -105,12 +105,16 @@ algorithm to set the priorities of the versions of a package.  Assign:
 <varlistentry>
 <term>priority 1</term>
 <listitem><simpara>to the versions coming from archives which in their <filename>Release</filename>
-files are marked as "NotAutomatic: yes" like the debian experimental archive.</simpara></listitem>
+files are marked as "NotAutomatic: yes" but <emphasis>not</emphasis> as "ButAutomaticUpgrades: yes"
+like the debian <literal>experimental</literal> archive.</simpara></listitem>
 </varlistentry>
 
 <varlistentry>
 <term>priority 100</term>
-<listitem><simpara>to the version that is already installed (if any).</simpara></listitem>
+<listitem><simpara>to the version that is already installed (if any) and to the versions coming
+from archives which in their <filename>Release</filename> files are marked as "NotAutomatic: yes" and
+"ButAutomaticUpgrades: yes" like the debian backports archive since <literal>squeeze-backports</literal>.
+</simpara></listitem>
 </varlistentry>
 
 <varlistentry>
@@ -129,7 +133,8 @@ files are marked as "NotAutomatic: yes" like the debian experimental archive.</s
 priority 100 to all installed package versions and priority 500 to all
 uninstalled package versions, except versions coming from archives which
 in their <filename>Release</filename> files are marked as "NotAutomatic: yes" -
-these versions get the priority 1.</para>
+these versions get the priority 1 or priority 100 if it is additionally marked
+as "ButAutomaticUpgrades: yes".</para>
 
 <para>APT then applies the following rules, listed in order of precedence,
 to determine which version of a package to install.