[gol8erl8]

@BetterRed Thanks again for the great information. This time, unfortunately, I tested it on A Tale of Two Cities, both the original and after Edit metadata in bulk, and got the following error message:

Spoiler:

calibre, version 4.10.1 (linux, embedded-python: False)
Failed to modify ePubs: Failed: Modify ePubs

Modify ePubs
Traceback (most recent call last):
  File "/usr/bin/calibre-parallel", line 20, in <module>
    sys.exit(main())
  File "/usr/lib64/calibre/calibre/utils/ipc/worker.py", line 208, in main
    result = func(*args, **kwargs)
  File "/usr/lib64/calibre/calibre/utils/ipc/worker.py", line 142, in arbitrary_n
    module = importlib.import_module(module_name)
  File "/usr/lib64/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 668, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 638, in _load_backward_compatible
  File "/usr/lib64/calibre/calibre/customize/zipplugin.py", line 184, in load_module
    exec(compiled, mod.__dict__)
  File "calibre_plugins.modify_epub.jobs", line 14, in <module>
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 668, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 638, in _load_backward_compatible
  File "/usr/lib64/calibre/calibre/customize/zipplugin.py", line 180, in load_module
    import_name), 'exec', dont_inherit=True)
  File "calibre_plugins.modify_epub.modify", line 479
    new_html = re.sub(r'<\?xml([^\?]*?)\?><', r'<?xml\1?>\n<', new_html)
                                                                       ^
TabError: inconsistent use of tabs and spaces in indentation

On another note, I noticed some neat-sounding options in the Modify ePub plugin, including Remove calibre bookmark files. I was bothered that calibre remembered the last page viewed without knowing where it saved this data or how to clear it. I suppose calibre is writing to the individual ebooks, or perhaps their separate metadata.opf, when you view them. However, I haven't done a hash check.