Merge pull request #2531 from rodrigoprimo/fix-valid-function-name-doc

NamingConventions/ValidFunctionName: update XML documentation

Author: jrfnl

WordPress/Docs/NamingConventions/ValidFunctionNameStandard.xml

@@ -24,16 +24,28 @@ function <em>Prefix_Function_NAME()</em> {}
         <code title="Valid: Words separated by underscores.">
         <![CDATA[
 class My_Class {
-    public static <em>method_name()</em> {}
+    public static function <em>method_name()</em> {}
 }
         ]]>
         </code>
         <code title="Invalid: Using camel case to separate words.">
         <![CDATA[
 class My_Class {
-    public static <em>methodName()</em> {}
+    public static function <em>methodName()</em> {}
 }
         ]]>
         </code>
     </code_comparison>
+    <code_comparison>
+        <code title="Valid: Single underscore prefix is allowed.">
+        <![CDATA[
+function <em>_prefix_function_name()</em> {}
+        ]]>
+        </code>
+        <code title="Invalid: Double underscore prefix is not allowed.">
+        <![CDATA[
+function <em>__prefix_function_name()</em> {}
+        ]]>
+        </code>
+    </code_comparison>
 </documentation>