Update the methodsynopsis of some recently changed stubs

Closes GH-625.

Author: kocsismate

reference/session/sessionhandler/read.xml

@@ -9,7 +9,7 @@
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>
-   <modifier>public</modifier> <type>string</type><methodname>SessionHandler::read</methodname>
+   <modifier>public</modifier> <type class="union"><type>string</type><type>false</type></type><methodname>SessionHandler::read</methodname>
    <methodparam><type>string</type><parameter>id</parameter></methodparam>
   </methodsynopsis>
   <para>
@@ -52,7 +52,7 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   Returns an encoded string of the read data. If nothing was read, it must return an empty string. Note this value is returned internally to PHP for processing.
+   Returns an encoded string of the read data. If nothing was read, it must return &false;. Note this value is returned internally to PHP for processing.
   </para>
  </refsect1>
 

reference/session/sessionhandlerinterface/read.xml

@@ -9,7 +9,7 @@
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>
-   <modifier>abstract</modifier> <modifier>public</modifier> <type>string</type><methodname>SessionHandlerInterface::read</methodname>
+   <modifier>public</modifier> <type class="union"><type>string</type><type>false</type></type><methodname>SessionHandlerInterface::read</methodname>
    <methodparam><type>string</type><parameter>id</parameter></methodparam>
   </methodsynopsis>
   <para>
@@ -22,7 +22,7 @@
    This method should retrieve the session data from storage by the
    session ID provided. The string returned by this method must be in the same
    serialized format as when originally passed to the <function>SessionHandlerInterface::write</function>
-   If the record was not found, return an empty string.
+   If the record was not found, return &false;.
   </para>
   <para>
    The data returned by this method will be decoded internally by PHP using the

reference/simplexml/simplexmlelement/addChild.xml

@@ -10,7 +10,7 @@
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>
-   <modifier>public</modifier> <type>SimpleXMLElement</type><methodname>SimpleXMLElement::addChild</methodname>
+   <modifier>public</modifier> <type class="union"><type>SimpleXMLElement</type><type>null</type></type><methodname>SimpleXMLElement::addChild</methodname>
    <methodparam><type>string</type><parameter>qualifiedName</parameter></methodparam>
    <methodparam choice="opt"><type class="union"><type>string</type><type>null</type></type><parameter>value</parameter><initializer>&null;</initializer></methodparam>
    <methodparam choice="opt"><type class="union"><type>string</type><type>null</type></type><parameter>namespace</parameter><initializer>&null;</initializer></methodparam>
@@ -56,7 +56,7 @@
   &reftitle.returnvalues;
   <para>
    The <literal>addChild</literal> method returns a <type>SimpleXMLElement</type>
-   object representing the child added to the XML node.
+   object representing the child added to the XML node on success; &null; on failure.
   </para>
  </refsect1>
 

reference/simplexml/simplexmlelement/xpath.xml

@@ -9,7 +9,7 @@
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>
-   <modifier>public</modifier> <type class="union"><type>array</type><type>false</type></type><methodname>SimpleXMLElement::xpath</methodname>
+   <modifier>public</modifier> <type class="union"><type>array</type><type>null</type><type>false</type></type><methodname>SimpleXMLElement::xpath</methodname>
    <methodparam><type>string</type><parameter>expression</parameter></methodparam>
   </methodsynopsis>
   <para>
@@ -37,7 +37,7 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   Returns an <type>array</type> of SimpleXMLElement objects or &false; in
+   Returns an <type>array</type> of SimpleXMLElement objects on success; or &null; or &false; in
    case of an error.
   </para>
  </refsect1>