docs: def register(self, path, help_text=None, help_context=None):
          """
          Registers email template.
  
          Example usage:
              email_templates.register('hello_template.html', help_text=u'Hello template',
                  help_context={'username': u'Name of user in hello expression'})
  
          :param path: Template file path. It will become immutable registry lookup key.
          :param help_text: Help text to describe template in admin site
          :param help_context: Dictionary of possible keys used in the context and description of their content
  
          `help_context` items values may be strings or tuples of two strings. If strings, then email template preview
          will use variable names to fill context, otherwise the second tuple element will become example value.
  
          If an email template is already registered, this will raise AlreadyRegistered.
          """
          if path in self._registry:
              raise AlreadyRegistered('The template %s is already registered' % path)
          self._registry[path] = RegistrationItem(path, help_text, help_context)
          logger.debug("Registered email template %s", path)