add code example to isDecoratedCall

javascript/ql/src/semmle/javascript/frameworks/HTTP.qll

@@ -237,6 +237,18 @@ module HTTP {
    * Holds if `call` decorates the function `pred`.
    * This means that `call` returns a function that forwards its arguments to `pred`.
    * Only holds when the decorator looks like it is decorating a route-handler.
+   *
+   * Below is a code example relating `call`, `decoratee`, `outer`, `inner`.
+   * ```
+   * function outer(method) {
+   *    return function inner(req, res) {
+   *      return method.call(this, req, res);
+   *    };
+   *  }
+   *  var route = outer(function decoratee(req, res) { // <- call
+   *    res.end("foo");
+   *  });
+   * ```
    */
   private predicate isDecoratedCall(DataFlow::CallNode call, DataFlow::FunctionNode decoratee) {
     // indirect route-handler `result` is given to function `outer`, which returns function `inner` which calls the function `pred`.