add example

Add an example serialization of node with attribute and value in same time

Author: pyatnitsev

components/serializer.rst

@@ -903,6 +903,18 @@ The array keys beginning with ``@`` are considered XML attributes::
     //     <foo bar="value" />
     // </response>
 
+If you want create a node with value and attribute use this::
+
+array('foo' => array('@bar' => 'value', # => 'baz'));
+
+    // is encoded as follows:
+    // <?xml version="1.0"?>
+    // <response>
+    //     <foo bar="value">
+    //        baz
+    //     </foo>
+    // </response>
+
 Context
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