class_docstr: A helper class that represents input list values that to be modified.
  
  Operations which modify field_value would generate new Field instance.
code: def __len__(self):
      return len(self.field_value)
  
file_path: textflint/textflint/input/component/field/list_field.py
imports: from .field import Field
  from ....common.utils.list_op import *
label_desc: Use image node_id 11 for calling the ListField obj's underlying member method code with example usage: obj.__len__() and returns: len