class_docstr: Problem spec for parsing tokenized Icelandic text to constituency trees.
code: def source_vocab_size(self):
      return 2**14
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.data_generators import text_problems
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import registry
label_desc: Use image node_id 1 for calling the ParsingIcelandic16k obj's underlying member method code with example usage: obj.source_vocab_size() and returns: unknown