Does the functions.php file ever get called during an AJAX call? Debug AJAX

Trying to figure out an issue a fellow programmer is having. I was wondering if the functions.php file get called at all when you do admin side AJAX? I know that when you do an AJAX call a part of WP gets loaded up to process the call and send back a response. Is the functions.php file included in that?

How Do I Use jQuery UI In My Plugin

It’s a sad day in the world when I Google something and it returns nothing. I am trying to use the default datepicker (or ANY datepicker at this point) and am unable to because of my lack of knowledge with WordPress/PHP. In my plugin, I am attempting to register jquery and the ui and apparently am breaking other parts of WordPress in the process. Can someone please tell me what I’m doing wrong and if they can provide a working solution, I will scrap all of my code:

Custom Taxonomy specific to a Custom Post type

I want to create a custom taxonomy which behaves similar to the post type as a category behaves to a the default posts (on the grounds of /%category%/%postname%/ permalink structure) so that the posts in the custom post types are displayed as
www.example.com/custom-post-type/custom-taxonomy-name/post-name
Also I want the category meta box to appear only when we add new default post and not when we add a new post in the custom post type and the custom taxonomy box to appear only when we add a new post in the custom post type and not when we add new a default post.

Query to sort a list by meta key first (if it exists), and show remaining posts without meta key ordered by title

I’m working on a custom taxonomy term page template where we want the items that are connected to the term sorted by a publication date (custom date field) – and if there are multiple items on the same day (formatted like YYYY-MM-DD) to then sort those by title, and finally sort by title if the custom field has not been filled out (older items).