minor #9249 Add example of setting the data of XML nodes (pyatnitsev, javiereguiluz)

This PR was submitted for the 4.0 branch but it was merged into the 3.4 branch instead (closes #9249).

Discussion
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Add example of setting the data of XML nodes

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

Commits
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7c862db Minor reword
d415361 fix minor syntax issue
51ba232 fix makeup
c4aecf4 add example

Author: javiereguiluz

components/serializer.rst

@@ -903,6 +903,18 @@ The array keys beginning with ``@`` are considered XML attributes::
     //     <foo bar="value" />
     // </response>
 
+Use the special ``#`` key to define the data of a node::
+
+    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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