Index: src/site/xdoc/manual/layouts.xml.vm
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- src/site/xdoc/manual/layouts.xml.vm	(date 1475431991000)
+++ src/site/xdoc/manual/layouts.xml.vm	(revision )
@@ -1403,9 +1403,9 @@
             <tr>
               <td align="center">
                 <a name="PatternMDC"/>
-                <b>X</b>{key[,key2...]}<br />
-                <b>mdc</b>{key[,key2...]}<br />
-                <b>MDC</b>{key[,key2...]}
+                <b>X</b>{key[,key2...]}[{defualtValue,[,defualtValue2...]}]<br />
+                <b>mdc</b>{key[,key2...]}[{defualtValue,[,defualtValue2...]}]<br />
+                <b>MDC</b>{key[,key2...]}[{defualtValue,[,defualtValue2...]}]
               </td>
               <td>
                 <p>Outputs the Thread Context Map (also known as the Mapped Diagnostic Context or MDC)
@@ -1417,7 +1417,8 @@
                   where
                   <code>clientNumber</code>
                   is the key. The value in the MDC
-                  corresponding to the key will be output.</p>
+                  corresponding to the key will be output. if you add another {} after the keys it will act like default values,
+                  if the key does not exist the default value will be writen. number of default values should be eqauls to numbers of keys.</p>
                 <p>If a list of keys are provided, such as <b>%X{name, number}</b>, then each key that is present in the
                     ThreadContext will be output using the format {name=val1, number=val2}. The key/value pairs will be
                   printed in the order they appear in the list.</p>