code: def forward(self, x, attention_mask, head_mask=None):
      all_features = (x,)
      all_attentions = ()
  
      for i, layer in enumerate(self.layers):
          mask = head_mask[i] if head_mask is not None else None
          layer_out = layer(x, attention_mask, mask)
  
          if self.output_hidden_feats:
              all_features = all_features + (x,)
          x = layer_out[0]
          if self.output_attentions:
              all_attentions = all_attentions + (layer_out[1],)
  
      outputs = (x,)
      if self.output_hidden_feats:
          outputs += (all_features,)
      if self.output_attentions:
          outputs += (all_attentions,)
      return outputs
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle.nn import ReLU, Swish, GELU
  import math
  from ppdet.core.workspace import register
  from ..shape_spec import ShapeSpec
label_desc: Use image node_id 2 for calling the BertEncoder obj's underlying member method code with example usage: obj.forward(x, attention_mask, head_mask) and returns: outputs