If I include Prototype and jQuery, why does inline jQuery conflict (over use of $) but not included jQuery files?

If Prototype is included in the page already, I have to do this:

jQuery(document).ready(function() 
{

for inline jQuery scripts instead of this:

$(document).ready(function() 
{

But if I have an included jQuery file on th开发者_如何学运维e same page that uses $, that does not seem to conflict, e.g.:

<script type='text/javascript' src='/js/included.js'></script>

In other words, I don't have to edit included.js and change all of the $ to jQuery.

Why the distinction: included files versus inline scripts?

---

included may be playing safe and deliberately shadowing $

(function($) {
  // included.js code here
})(jQuery);