Document that interfaces can be extended + usage example

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@264647 c90b9560-bf6c-de11-be94-00142212c4b1

language/oop5/interfaces.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.10 $ -->
+<!-- $Revision: 1.11 $ -->
  <sect1 xml:id="language.oop5.interfaces" xmlns="http://docbook.org/ns/docbook">
   <title>Object Interfaces</title>
   <para>
@@ -30,6 +30,12 @@
      it would cause ambiguity.
     </para>
    </note>
+   <note>
+    <para>
+     Interfaces can be extended like classes using the <literal>extend</literal> 
+     operator.
+    </para>
+   </note>
   </sect2>
   <sect2 xml:id="language.oop5.interfaces.examples">
    &reftitle.examples;
@@ -83,6 +89,46 @@ class BadTemplate implements iTemplate
 ]]>
     </programlisting>
    </example>
+   <example xml:id="language.oop5.interfaces.examples.ex2">
+    <title>Extendable Interfaces</title>
+     <programlisting role="php">
+<![CDATA[
+interface a
+{
+    public function foo();
+}
+
+interface b extends a
+{
+    public function baz(Baz $baz);
+}
+
+// This will work
+class c implements b
+{
+    public function foo()
+    {
+    }
+
+    public function baz(Baz $baz)
+    {
+    }
+}
+
+// This will not work and result in a fatal error
+class d implements b
+{
+    public function foo()
+    {
+    }
+
+    public function baz(Foo $foo)
+    {
+    }
+}
+]]>
+     </programlisting>
+   </example>
    <simpara>
      See also the <link linkend="language.operators.type">instanceof</link>
      operator.