docs: def init_config(self, app):
          """Initialize configuration.
  
          :param app: An instance of :class:`~flask.Flask`.
          """
          _vars = ['BASE_TEMPLATE', 'COVER_TEMPLATE', 'SETTINGS_TEMPLATE']
  
          # Sets RequireJS config and SASS binary as well if not already set.
          for k in dir(config):
              if k.startswith('THEME_') or k in [
                      'REQUIREJS_CONFIG', 'SASS_BIN'] + _vars:
                  app.config.setdefault(k, getattr(config, k))
  
          # Set THEME_<name>_TEMPLATE from <name>_TEMPLATE variables if not
          # already set.
          for varname in _vars:
              theme_varname = 'THEME_{}'.format(varname)
              if app.config[theme_varname] is None:
                  app.config[theme_varname] = app.config[varname]
  
          app.config.setdefault(
              'ADMIN_BASE_TEMPLATE', config.ADMIN_BASE_TEMPLATE)