If you are using theme_get_settings, such as: $value = trim(theme_get_setting('my_setting')); Then in your code editor you will also be seeing undefined  function 'theme_get_setting'.  This function has been deprecated for some time.   Instead, you need to use Passing the theme.manager and theme.initialization services to theme_handler constructor as optional parameters is deprecated. These parameters are also mandatory. $theme_handler = \Drupal::service('theme_handler');Get...

Using shell access you the site you want to add the Spyc library.  Then go to the libraries directory and add the following commands: mkdir spyc cd spyc wget https://github.com/mustangostang/spyc/blob/master/Spyc.phpTo verify that Spyc is active, go to the status area of admin (admin/reports/status)