WordPress at a glance
action is not described

upload_ui_over_quota action-hook . WP 3.5.0

Fires when an upload will exceed the defined upload space quota for a network site.

Usage

add_action( 'upload_ui_over_quota', 'action_function_name_795' );
function action_function_name_795(){
	// action...
}

Where the hook is called

media_upload_form()
wp_print_media_templates()
wp-admin/includes/media.php 1843
do_action( 'upload_ui_over_quota' );
wp-includes/media-template.php 199
do_action( 'upload_ui_over_quota' ); ?>

Where the hook is used (in WP core)

wp-includes/ms-default-filters.php 73
add_action( 'upload_ui_over_quota', 'multisite_over_quota_message' );