code: def _subword_start_by_spacer(tokens: Sequence[str]) -> Sequence[bool]:
      """Find word start in a subword list marked by spacer(as prefix)."""
      flag = [x.startswith(SubwordMarker.SPACER) for x in tokens]
      flag[0] = True
      return flag
  
imports: import math
  import numpy
  import torch
  from typing import Sequence, Callable
  from onmt.constants import DefaultTokens, SubwordMarker
  from onmt.transforms import register_transform
  from .transform import Transform
label_desc: Use image node_id 2 for calling a global function with example usage: _subword_start_by_spacer(tokens) and returns: flag