Collection of useful functions for Wordpress Just drop in functions.php

acf_add_options_sub_page.php

if( function_exists('acf_add_options_sub_page') )
{
	acf_add_options_sub_page( 'General' );
  acf_add_options_sub_page( 'Kontakt Intros' );
}

add_current_nav_class.php

function add_current_nav_class($classes, $item) {
	
	// Getting the current post details
	global $post;
	
	// Getting the post type of the current post
	$current_post_type = get_post_type_object(get_post_type($post->ID));
	$current_post_type_slug = $current_post_type->rewrite[slug];
		
	// Getting the URL of the menu item
	$menu_slug = strtolower(trim($item->url));
	
	// If the menu item URL contains the current post types slug add the current-menu-item class
	if (strpos($menu_slug,$current_post_type_slug) !== false) {
	
	   $classes[] = 'current-menu-item';
	
	}
	// Return the corrected set of classes to be added to the menu item
	return $classes;

}
add_action('nav_menu_css_class', 'add_current_nav_class', 10, 2 );

allow_svg.php

function cc_mime_types($mimes) {
  $mimes['svg'] = 'image/svg+xml';
  return $mimes;
}
add_filter('upload_mimes', 'cc_mime_types');

function custom_admin_head() {
  $css = '';

  $css = 'td.media-icon img[src$=".svg"] { width: 100% !important; height: auto !important; }';

  echo '<style type="text/css">'.$css.'</style>';
}
add_action('admin_head', 'custom_admin_head');

get_id_by_slug.php

function get_id_by_slug($page_slug) {
    $page = get_page_by_path($page_slug);
    if ($page) {
        return $page->ID;
    } else {
        return null;
    }
}