improve ARM text about cache DB statistics

diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index ab2222d67c961223942162975dec17138e48ba06..c735a357964441a26fd5b69453e3ace31e155547 100644 (file)
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -15227,15 +15227,29 @@ HOST-127.EXAMPLE. MX 0 .
                </entry>
                <entry colname="2">
                  <para>
-                   The number of RRsets per RR type and nonexistent
-                   names stored in the cache database.
-                   If the exclamation mark (!) is printed for a RR
-                   type, it means that particular type of RRset is
-                   known to be nonexistent (this is also known as
-                   "NXRRSET").  If a hash mark (#) is present then
-                   the RRset is stale.  If a tilde mark (~) is
-                   present, the RRset is marked for garbage
-                   collection.  Maintained per view.
+                   Statistics counters related to cache contents;
+                   maintained per view.
+                 </para>
+                 <para>
+                   The "NXDOMAIN" counter is the number of names
+                   that have been cached as nonexistent.
+                   Counters named for RR types indicate the
+                   number of active RRsets for each type in the cache
+                   database.
+                 </para>
+                 <para>
+                   If an RR type name is preceded by an exclamation
+                   mark (!), it represents the number of records in the
+                   cache which indicate that the type does not exist
+                   for a particular name (this is also known as "NXRRSET").
+                   If an RR type name is preceded by a hash mark (#), it
+                   represents the number of RRsets for this type that are
+                   present in the cache but whose TTLs have expired; these
+                   RRsets may only be used if stale answers are enabled.
+                   If an RR type name is preceded by a tilde (~), it
+                   represents the number of RRsets for this type that are
+                   present in the cache database but are marked for garbage
+                   collection; these RRsets cannot be used.
                  </para>
                </entry>
              </row>