[master] more prefetch doc improvement

diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 0af06cea119b200dce7d3cf1730397df6d9a0b0e..61eeb8ca3347971b66bb8aa2c79a066f742495b4 100644 (file)
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -8953,17 +8953,20 @@ avoid-v6-udp-ports { 40000; range 50000 60000; };
                  query will take place: when a cache record with a
                  lower TTL value is encountered during query processing,
                  it will be refreshed.  Valid trigger TTL values are 1 to
-                 10 seconds.  Setting a trigger TTL to zero (0) causes
+                 10 seconds.  Values larger than 10 seconds will be silently
+                 reduced to 10.
+                 Setting a trigger TTL to zero (0) causes
                  prefetch to be disabled.
                  The default trigger TTL is <literal>2</literal>.
                </para>
                <para>
-                 An optional second argument can be used
-                 to set the smallest <emphasis>original</emphasis>
+                 An optional second argument specifies the "eligibility"
+                 TTL: the smallest <emphasis>original</emphasis>
                  TTL value that will be accepted for a record to be
-                 eligible for prefetching.  The difference between
-                 the trigger TTL and the eligibility TTL must be
-                 at least 6 seconds.  
+                 eligible for prefetching.  The eligibility TTL must
+                 be at least six seconds longer than the trigger TTL;
+                 if it isn't, <command>named</command> will silently
+                 adjust it upward.
                  The default eligibility TTL is <literal>9</literal>.
                </para>
              </listitem>