class_docstr: A logging filter designed to record missing reference warning messages
  for use by this extension
code: def __init__(self, app):
      self.app = app
      super().__init__()
  
imports: from collections import defaultdict
  import json
  import logging
  from pathlib import Path
  from docutils.utils import get_source_line
  from docutils import nodes
  from sphinx.util import logging
  import matplotlib
label_desc: Use image node_id 1 to create a new MissingReferenceFilter object from inherited base classes: logging with example: obj = MissingReferenceFilter(app)