diff --git a/reference/xmlwriter/setup.xml b/reference/xmlwriter/setup.xml
index ceb1326343..6b637bdd23 100644
--- a/reference/xmlwriter/setup.xml
+++ b/reference/xmlwriter/setup.xml
@@ -14,6 +14,11 @@
  <!-- {{{ Installation -->
  <section xml:id="xmlwriter.installation">
   &reftitle.install;
+  <para>
+   The XMLWriter extension was initially a PECL extension for PHP 5. It
+   was later added to the PHP source (bundled) as of PHP 5.1.2. This
+   extension is enabled by default.
+  </para>
   <para>
    &installation.enabled.disable;
    <option role="configure">--disable-xmlwriter</option>