code: def _plot_sources(self) -> List[str]:
      from dvc.repo.plots import _collect_pipeline_files
  
      sources: List[str] = []
      for data in _collect_pipeline_files(self.repo, [], {}).values():
          for plot_id, props in data.get("data", {}).items():
              if isinstance(props.get("y"), dict):
                  sources.extend(props["y"])
                  if isinstance(props.get("x"), dict):
                      sources.extend(props["x"])
              else:
                  sources.append(plot_id)
      return sources
  
imports: import logging
  import time
  from collections import defaultdict
  from functools import partial
  from itertools import chain
  from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, Iterator, List, NamedTuple, Optional, Set, Tuple, Union
  from funcy.debug import format_time
  from dvc.dependency import ParamsDependency
  from dvc.fs import LocalFileSystem
  from dvc.fs.callbacks import DEFAULT_CALLBACK
  from dvc.log import logger
  from dvc.utils.objects import cached_property
label_desc: Use image node_id 18 for calling the Index obj's underlying member method code with example usage: obj._plot_sources() and returns: sources