code: def backward_word(event):
      """
      Move back to the start of the current or previous word. Words are composed
      of letters and digits.
      """
      buff = event.current_buffer
      pos = buff.document.find_previous_word_beginning(count=event.arg)
  
      if pos:
          buff.cursor_position += pos
  
imports: from __future__ import unicode_literals
  from prompt_toolkit.enums import IncrementalSearchDirection, SEARCH_BUFFER
  from prompt_toolkit.selection import PasteMode
  from six.moves import range
  import six
  from .completion import generate_completions, display_completions_like_readline
  from prompt_toolkit.document import Document
  from prompt_toolkit.enums import EditingMode
  from prompt_toolkit.key_binding.input_processor import KeyPress
  from prompt_toolkit.keys import Keys
label_desc: Use image node_id 8 for calling a global function with example usage: backward_word(event) without return types