Where does the gallery shortcode gets its attachments from?

Question

I know that media are an attachment post type that are children to a post, but how are galleries stored in WordPress?

Answer 1

This completely depends on how your gallery shortcode looks like.

If you replaced it with something custom, then you'll have to take a look at the plugin (or the theme).

The default gallery shortcode gets it from a query:

$query_args = array(
     'post_status'    => 'inherit'
    ,'post_type'      => 'attachment'
    ,'post_mime_type' => 'image'
    ,'order'          => $order
    ,'orderby'        => $orderby
);

Then it decides to add additional args for either include or exclude.

Here're the 3 scenarios that add the additional/non-shared arguments.

'include' => preg_replace( '/[^\D,]+/', '', $include )
'exclude' => preg_replace( '/[^\D,]+/', '', $include )
// default
'post_parent' => $id