class_docstr: Builder that outputs epub3 files.
  
  It creates the metainfo files content.opf, nav.xhtml, toc.ncx, mimetype,
  and META-INF/container.xml. Afterwards, all necessary files are zipped to
  an epub file.
class_docstr_tok: ["Builder","that","outputs","epub3","files",".","It","creates","the","metainfo","files","content.opf",",","nav.xhtml",",","toc.ncx",",","mimetype",",","and","META-INF\/container.xml",".","Afterwards",",","all","necessary","files","are","zipped","to","an","epub","file","."]
docstr: Write the metainfo file nav.xhtml.
docstr_tok: ["Write","the","metainfo","file","nav.xhtml","."]
code: def build_navigation_doc(self) -> None:
      """Write the metainfo file nav.xhtml."""
      logger.info(__("writing nav.xhtml file..."))
  
      if self.config.epub_tocscope == "default":
          doctree = self.env.get_and_resolve_doctree(
              self.config.root_doc,
              self,
              prune_toctrees=False,
              includehidden=False,
          )
          refnodes = self.get_refnodes(doctree, [])
          self.toc_add_files(refnodes)
      else:
          # 'includehidden'
          refnodes = self.refnodes
      navlist = self.build_navlist(refnodes)
      copy_asset_file(
          path.join(self.template_dir, "nav.xhtml_t"),
          self.outdir,
          self.navigation_doc_metadata(navlist),
      )
  
      # Add nav.xhtml to epub file
      if "nav.xhtml" not in self.files:
          self.files.append("nav.xhtml")
  
imports: from __future__ import annotations
  import html
  import os
  import re
  import time
  from os import path
  from typing import TYPE_CHECKING, Any, NamedTuple
  from sphinx import package_dir
  from sphinx.builders import _epub_base
  from sphinx.config import ENUM, Config
  from sphinx.locale import __
  from sphinx.util import logging
  from sphinx.util.fileutil import copy_asset_file
  from sphinx.util.osutil import make_filename
label_desc: Use image node_id 6 for calling the Epub3Builder obj's underlying member method code with example usage: obj.build_navigation_doc() without return types