WordPress at a glance
function is not described

check_upload_mimes() WP 3.0.0

Check an array of MIME types against a whitelist.

WordPress ships with a set of allowed upload filetypes, which is defined in wp-includes/functions.php in get_allowed_mime_types(). This function is used to filter that list against the filetype whitelist provided by Multisite Super Admins at wp-admin/network/settings.php.

No Hooks.

Return

Array.

Usage

check_upload_mimes( $mimes );
$mimes(array) (required)

Code of check upload mimes: wp-includes/ms-functions.php VER 5.0.3

<?php
function check_upload_mimes( $mimes ) {
	$site_exts = explode( ' ', get_site_option( 'upload_filetypes', 'jpg jpeg png gif' ) );
	$site_mimes = array();
	foreach ( $site_exts as $ext ) {
		foreach ( $mimes as $ext_pattern => $mime ) {
			if ( $ext != '' && strpos( $ext_pattern, $ext ) !== false )
				$site_mimes[$ext_pattern] = $mime;
		}
	}
	return $site_mimes;
}