diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index 80a9197..96df9b4 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -36,9 +36,12 @@
       <action dev="ggregory" type="update" issue="CONFIGURATION-752" due-to="Gary Gregory">
         Update Apache Commons VFS from 2.3 to 2.4.
       </action>
-      <action dev="ggregory" type="update" due-to="Gary Gregory">
+      <action dev="ggregory" type="fix" due-to="Gary Gregory">
         Fix Javadoc for org.apache.commons.configuration2.PropertiesConfiguration.getIncludeOptional().
       </action>
+      <action dev="ggregory" type="add" due-to="Gary Gregory">
+        Document "includeOptional" on the site.
+      </action>
     </release>
     <release version="2.5" date="2019-05-23"
              description="Minor release with new features and updated dependencies.">
diff --git a/src/site/xdoc/userguide/howto_properties.xml b/src/site/xdoc/userguide/howto_properties.xml
index a4200cb..4461b16 100644
--- a/src/site/xdoc/userguide/howto_properties.xml
+++ b/src/site/xdoc/userguide/howto_properties.xml
@@ -94,8 +94,14 @@
       <subsection name="Includes">
         <p>
           If a property is named "<code>include</code>", and the value of that property is the
-          name of a file on the disk, that file will be included into the configuration. Here is
-          an example:
+          name of a file on the disk, that file will be included into the configuration. 
+        </p>
+        <p>
+          The difference between "<code>include</code>" and "<code>includeOptional</code>" (below) is that if the file value 
+          is absent, processing continues with "<code>includeOptional</code>" but stops with "<code>include</code>".
+        </p>
+        <p>
+          For example:
         </p>
 <source>
 # usergui.properties
@@ -112,6 +118,33 @@
 
       </subsection>
 
+      <subsection name="Oprional Includes">
+        <p>
+          If a property is named "<code>includeOptional</code>", and the value of that property is the
+          name of a file on the disk, that file will be included into the configuration.
+        </p>
+        <p>
+          The difference between "<code>include</code>" (above) and "<code>includeOptional</code>" is that if the file value 
+          is absent, processing continues with "<code>includeOptional</code>" but stops with "<code>include</code>".
+        </p>
+        <p>
+          For example:
+        </p>
+<source>
+# usergui.properties
+
+includeOptional = colors.properties
+includeOptional = sizes.properties
+</source>
+
+<source>
+# colors.properties
+
+colors.background = #FFFFFF
+</source>
+
+      </subsection>
+
       <subsection name="Lists and arrays">
         <p>
           As was already pointed out in the section