Add event handler example to documentation on how to programmatically access a selection data.

docs/_includes/options/data/selection-access.html

@@ -35,6 +35,16 @@ $('select').select2({
 
 // Retrieve custom attribute value of the first selected element
 $('select').find(':selected').attr('data-custom-attribute')
+{% endhighlight %}
+
+  <p>
+    In addition, properties/values from source data objects can ba accessed from within event handler:
+  </p>
+
+{% highlight js linenos %}
+$('select').on('select2:select', function (event) {
+  console.log(event.params.data)
+});
 {% endhighlight %}
 
 </section>