#28: autocomplete_users_for_site_admins

autocomplete_users_for_site_admins.php

<?php
/**
 * Enable user auto-complete for non-super admins who have the promote_users cap.
 * 
 * @see wp_ajax_autocomplete_user()
 * 
 * @param bool $yesno Whether to allow non-super admins to use user autocomplete. Defaults to false.
 * 
 * @return bool Whether to allow it.
 */
function wpdocs_ms_user_autocomplete( $yesno ) {
	if ( current_user_can( 'promote_users' ) )
		return true;
	else
		return false;
}
add_filter( 'autocomplete_users_for_site_admins', 'wpdocs_ms_user_autocomplete' );