class_docstr: Domain for citations.
class_docstr_tok: ["Domain","for","citations","."]
code: def note_citation_reference(self, node: pending_xref) -> None:
      docnames = self.citation_refs.setdefault(node["reftarget"], set())
      docnames.add(self.env.docname)
  
imports: from __future__ import annotations
  from typing import TYPE_CHECKING, Any, cast
  from docutils import nodes
  from sphinx.addnodes import pending_xref
  from sphinx.domains import Domain
  from sphinx.locale import __
  from sphinx.transforms import SphinxTransform
  from sphinx.util import logging
  from sphinx.util.nodes import copy_source_info, make_refnode
label_desc: Use image node_id 6 for calling the CitationDomain obj's underlying member method code with example usage: obj.note_citation_reference(node) without return types