docs: def activate(ctx):
          """Activate the given ParseContext."""
          if hasattr(ctx, '_on_context_exit'):
              raise ContextError(
                  'Context actions registered outside this '
                  'parse context are active')
  
          try:
              ParseContext._active.append(ctx)
              ctx._on_context_exit = []
              yield
          finally:
              for func, args, kwargs in ctx._on_context_exit:
                  func(*args, **kwargs)
              del ctx._on_context_exit
              ParseContext._active.pop()