code: def forward(self, rois_feat, stage=0):
      out = self.head_list[stage](rois_feat)
      return out
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle.nn.initializer import Normal
  from ppdet.core.workspace import register
  from .bbox_head import BBoxHead, TwoFCHead, XConvNormHead
  from .roi_extractor import RoIAlign
  from ..shape_spec import ShapeSpec
  from ..bbox_utils import delta2bbox, clip_bbox, nonempty_bbox
  from ..cls_utils import _get_class_default_kwargs
label_desc: Use image node_id 4 for calling the CascadeXConvNormHead obj's underlying member method code with example usage: obj.forward(rois_feat, stage) and returns: out