code: def forward(model, trf_full, is_train):
      def backprop(d_trf_datas):
          return trf_full.unsplit_by_doc(
              [x.tensors for x in d_trf_datas]
          )
  
      return trf_full.doc_data, backprop
  
imports: from thinc.api import Model
  from typing import List
  from ..data_classes import FullTransformerBatch, TransformerData
label_desc: Use image node_id 2 for calling a global function with example usage: forward(model, trf_full, is_train) and returns: trf_full,  backprop, trf_full