diff --git a/introduction/important/building-notes.xml b/introduction/important/building-notes.xml
index f7cad62f95..6a1ced755a 100644
--- a/introduction/important/building-notes.xml
+++ b/introduction/important/building-notes.xml
@@ -455,6 +455,19 @@ chmod 755 blfs-yes-test2</userinput></screen>
         installed, except if the dependency is said to be
         <quote>runtime</quote>, which means the target package can be built but
         cannot function without it.</para>
+        <para>
+          Note that a target package can start to <quote>function</quote>
+          in many subtle ways: an installed configuration file can make the
+          init system, cron daemon, or bus daemon to run a program
+          automatically; another package using the target package as an
+          dependency can run a program from the target package in the
+          building system; and the configuration sections in the BLFS book
+          may also run a program from a just installed package.  So if
+          you are installing the target package without a
+          <emphasis>Required (runtime)</emphasis> dependency installed,
+          You should install the dependency as soon as possible after the
+          installation of the target package.
+        </para>
       </listitem>
       <listitem>
         <para><emphasis>Recommended</emphasis> means that BLFS strongly
@@ -471,31 +484,20 @@ chmod 755 blfs-yes-test2</userinput></screen>
       <listitem>
         <para><emphasis>Optional</emphasis> means that this package might be
         installed for added functionality. Often BLFS will describe the
-        dependency to explain the added functionality that will result.</para>
-      </listitem>
-      <listitem>
-        <para><emphasis>Runtime</emphasis> means this package is not needed
-        to install the target package, but when you run a program from the
-        target package or a program using a library from the target
-        package, it may lack some functionality or even crash immediately.
-        Based on the importance of the lacked functionality, the Runtime
-        dependencies are further labeled as Required, Recommended, or
-        Optional.  You can install a Runtime dependency to recover the
-        lacked functionality of the target package, without rebuilding the
-        target package itself.</para>
-        <para>
-          Note that a target package can start to <quote>run</quote> in
-          many subtle ways: an installed configuration file can make the
-          init system, cron daemon, or bus daemon to run a program
-          automatically; another package using the target package as an
-          dependency can run a program from the target package in the
-          building system; and the configuration sections in the BLFS book
-          may also run a program from a just installed package.  So if
-          you are installing the target package without a
-          <emphasis>Required (Runtime)</emphasis> dependency installed,
-          You should install the dependency as soon as possible after the
-          installation of the target package.
-        </para>
+        dependency to explain the added functionality that will result.
+        An optional dependency may be automatically pick up by the target
+        package if the dependency is installed, but another some optional
+        dependency may also need additional configuration options to enable
+        them when the target package is built.  Such additional options are
+        often documented in the BLFS book.  If an optional dependency is
+        said to be <quote>runtime</quote>, it means you may install
+        the dependency after installing the target package to support some
+        optional features of the target package if you need these
+        features.</para>
+        <para>An optional dependency may be out of BLFS.  If you need such
+        an <emphasis>external</emphasis> optional dependency for some
+        features you need, read <xref linkend='beyond'/> for the general
+        hint about installing an out-of-BLFS package.</para>
       </listitem>
     </itemizedlist>