diff --git a/reference/pdo/constants.xml b/reference/pdo/constants.xml
index 8039f4d652..f3ae494648 100644
--- a/reference/pdo/constants.xml
+++ b/reference/pdo/constants.xml
@@ -101,6 +101,7 @@
      Specifies that the fetch method shall return each row as an object with
      variable names that correspond to the column names returned in the result
      set. <constant>PDO::FETCH_LAZY</constant> creates the object variable names as they are accessed.
+     Not valid inside <function>PDOStatement::fetchAll</function>.
     </simpara>
    </listitem>
   </varlistentry>
@@ -237,7 +238,8 @@
    </term>
    <listitem>
     <simpara>
-
+     Allows completely customize the way data is treated on the fly (only 
+     valid inside <function>PDOStatement::fetchAll</function>).
     </simpara>
    </listitem>
   </varlistentry>
@@ -248,7 +250,9 @@
    </term>
    <listitem>
     <simpara>
-
+     Group return by values. Usually combined with
+     <constant>PDO::FETCH_COLUMN</constant> or 
+     <constant>PDO::FETCH_KEY_PAIR</constant>.
     </simpara>
    </listitem>
   </varlistentry>
@@ -259,7 +263,7 @@
    </term>
    <listitem>
     <simpara>
-
+     Fetch only the unique values.
     </simpara>
    </listitem>
   </varlistentry>