diff --git a/reference/xmlwriter/functions/xmlwriter-start-attribute-ns.xml b/reference/xmlwriter/functions/xmlwriter-start-attribute-ns.xml
index ff5d33e096..d251e59d71 100644
--- a/reference/xmlwriter/functions/xmlwriter-start-attribute-ns.xml
+++ b/reference/xmlwriter/functions/xmlwriter-start-attribute-ns.xml
@@ -14,7 +14,7 @@
    <type>bool</type><methodname>XMLWriter::startAttributeNs</methodname>
    <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
   </methodsynopsis>
   <para>&style.procedural;</para>
   <methodsynopsis>
@@ -22,7 +22,7 @@
    <methodparam><type>resource</type><parameter>xmlwriter</parameter></methodparam>
    <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
   </methodsynopsis>
   <para>
    Starts a namespaced attribute.
@@ -54,6 +54,8 @@
      <listitem>
       <para>
        The namespace URI.
+       If <parameter>uri</parameter> is &null;, the namespace declaration will be
+       omitted.
       </para>
      </listitem>
     </varlistentry>
diff --git a/reference/xmlwriter/functions/xmlwriter-start-element-ns.xml b/reference/xmlwriter/functions/xmlwriter-start-element-ns.xml
index c7abe2ae1e..cbcefe1bcb 100644
--- a/reference/xmlwriter/functions/xmlwriter-start-element-ns.xml
+++ b/reference/xmlwriter/functions/xmlwriter-start-element-ns.xml
@@ -12,17 +12,17 @@
   <para>&style.oop;</para>
   <methodsynopsis>
    <type>bool</type><methodname>XMLWriter::startElementNs</methodname>
-   <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
   </methodsynopsis>
   <para>&style.procedural;</para>
   <methodsynopsis>
    <type>bool</type><methodname>xmlwriter_start_element_ns</methodname>
    <methodparam><type>resource</type><parameter>xmlwriter</parameter></methodparam>
-   <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
   </methodsynopsis>
   <para>
    Starts a namespaced element.
@@ -38,6 +38,7 @@
      <listitem>
       <para>
        The namespace prefix.
+       If <parameter>prefix</parameter> is &null;, the namespace will be omitted.
       </para>
      </listitem>
     </varlistentry>
@@ -54,6 +55,8 @@
      <listitem>
       <para>
        The namespace URI.
+       If <parameter>uri</parameter> is &null;, the namespace declaration will be
+       omitted.
       </para>
      </listitem>
     </varlistentry>
diff --git a/reference/xmlwriter/functions/xmlwriter-write-attribute-ns.xml b/reference/xmlwriter/functions/xmlwriter-write-attribute-ns.xml
index eb96ac723a..f777f66d0e 100644
--- a/reference/xmlwriter/functions/xmlwriter-write-attribute-ns.xml
+++ b/reference/xmlwriter/functions/xmlwriter-write-attribute-ns.xml
@@ -12,18 +12,18 @@
   <para>&style.oop;</para>
   <methodsynopsis>
    <type>bool</type><methodname>XMLWriter::writeAttributeNs</methodname>
-   <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
    <methodparam><type>string</type><parameter>content</parameter></methodparam>
   </methodsynopsis>
   <para>&style.procedural;</para>
   <methodsynopsis>
    <type>bool</type><methodname>xmlwriter_write_attribute_ns</methodname>
    <methodparam><type>resource</type><parameter>xmlwriter</parameter></methodparam>
-   <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
    <methodparam><type>string</type><parameter>content</parameter></methodparam>
   </methodsynopsis>
   <para>
@@ -40,6 +40,7 @@
      <listitem>
       <para>
        The namespace prefix.
+       If <parameter>prefix</parameter> is &null;, the namespace will be omitted.
       </para>
      </listitem>
     </varlistentry>
@@ -56,6 +57,8 @@
      <listitem>
       <para>
        The namespace URI.
+       If <parameter>uri</parameter> is &null;, the namespace declaration will be
+       omitted.
       </para>
      </listitem>
     </varlistentry>
diff --git a/reference/xmlwriter/functions/xmlwriter-write-element-ns.xml b/reference/xmlwriter/functions/xmlwriter-write-element-ns.xml
index 440b94c87b..d1fb98fde9 100644
--- a/reference/xmlwriter/functions/xmlwriter-write-element-ns.xml
+++ b/reference/xmlwriter/functions/xmlwriter-write-element-ns.xml
@@ -12,19 +12,19 @@
   <para>&style.oop;</para>
   <methodsynopsis>
    <type>bool</type><methodname>XMLWriter::writeElementNs</methodname>
-   <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
-   <methodparam choice="opt"><type>string</type><parameter>content</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
+   <methodparam choice="opt"><type>string</type><parameter>content</parameter><initializer>&null;</initializer></methodparam>
   </methodsynopsis>
   <para>&style.procedural;</para>
   <methodsynopsis>
    <type>bool</type><methodname>xmlwriter_write_element_ns</methodname>
    <methodparam><type>resource</type><parameter>xmlwriter</parameter></methodparam>
-   <methodparam><type>string</type><parameter>prefix</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>prefix</parameter></methodparam>
    <methodparam><type>string</type><parameter>name</parameter></methodparam>
-   <methodparam><type>string</type><parameter>uri</parameter></methodparam>
-   <methodparam choice="opt"><type>string</type><parameter>content</parameter></methodparam>
+   <methodparam><type class="union"><type>string</type><type>null</type></type><parameter>uri</parameter></methodparam>
+   <methodparam choice="opt"><type>string</type><parameter>content</parameter><initializer>&null;</initializer></methodparam>
   </methodsynopsis>
   <para>
    Writes a full namespaced element tag.
@@ -40,6 +40,7 @@
      <listitem>
       <para>
        The namespace prefix.
+       If <parameter>prefix</parameter> is &null;, the namespace will be omitted.
       </para>
      </listitem>
     </varlistentry>
@@ -56,6 +57,8 @@
      <listitem>
       <para>
        The namespace URI.
+       If <parameter>uri</parameter> is &null;, the namespace declaration will be
+       omitted.
       </para>
      </listitem>
     </varlistentry>