When I downloaded the latest version 3.8.1, inside wp-include/js there is a jQuery folder.
Can I assume that WordPress will always include it, meaning I don’t have to make my own call? E.g.
wp_register_script('jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js', array(), null, false);
wp_enqueue_script('jquery');
Yes, jQuery is part of WordPress core. But–it can become outdated, because jQuery updates can happen in between WP releases. The recent release of WordPress does use a very recent version of jQuery.
By default,
wp_enqueue_script('jquery')
grabs jQuery from the core at /wp-includes/js/jquery/jquery.js.
The “correct” way to add jQuery to your WP site is:
function theme_scripts() {
wp_enqueue_script('jquery');
}
add_action('wp_enqueue_scripts', 'theme_scripts');
Another catch–if you do use the latest jQuery, be careful that it doesn’t break plugins.