docs: def ga_context(context_func):
      """
      A decorator for Cornice views that allows one to set extra parameters
      for Google Analytics tracking::
  
          @ga_context(lambda context: {'dt': context['category'].title, })
          @view_config(route_name='page')
          def view(request):
              return {
                  'category': self.workspace.S(Category).filter(title='foo')[0],
              }
  
      :param func context_func:
          A function which takes one argument, a context dictionary made
          available to the template.
      :returns:
          A dict containing the extra variables for Google Analytics
          tracking.
      """
      def decorator(func):
          @wraps(func)
          def wrapper(self, *args, **kwargs):
              context = func(self, *args, **kwargs)
              self.request.google_analytics.update(context_func(context))
              return context
          return wrapper
      return decorator