code: def wysiwyg_static_url(appname, prefix, default_path):
      
      if appname in settings.INSTALLED_APPS:
          return urljoin(settings.STATIC_URL, prefix)
      else:
          return default_path
docs: Automatically use an prefix if a given application is installed.
      For example, if django-ckeditor is installed, use it's STATIC_URL/ckeditor folder to find the CKEditor distribution.
      When the application does not available, fallback to the default path.
  
      This is a function for the internal templates of *django-wysiwyg*.