class_docstr: An abstract class that represents constraints which are applied before
  the transformation.
  
  These restrict which words are allowed to be modified during the
  transformation. For example, we might not allow stopwords to be
  modified.
docstr: Returns the word indices in ``current_text`` which are able to be
  modified. Must be overridden by specific pre-transformation
  constraints.
  
  Args:
      current_text: The ``AttackedText`` input to consider.
code: def _get_modifiable_indices(current_text):
      """Returns the word indices in ``current_text`` which are able to be
      modified. Must be overridden by specific pre-transformation
      constraints.
  
      Args:
          current_text: The ``AttackedText`` input to consider.
      """
      raise NotImplementedError()
  
file_path: TextAttack/textattack/constraints/pre_transformation_constraint.py
imports: from abc import ABC, abstractmethod
  from textattack.shared.utils import ReprMixin
label_desc: Use image node_id 2 for calling the PreTransformationConstraint obj's underlying member method code with example usage: obj._get_modifiable_indices(current_text) without return types