ModuleNotFoundError for extensions=['outline']

[jonathanunderwood]

The docs for this state that to use the extension you should do md.markdown(s, extensions=['outline',] which results in:

ModuleNotFoundError                       Traceback (most recent call last)
<ipython-input-44-e4a1d7afe35e> in <module>
----> 1 md.markdown(s, extensions=['tables', 'outline',])

~/.virtualenvs/ontology/lib/python3.7/site-packages/markdown/core.py in markdown(text, **kwargs)
    388 
    389     """
--> 390     md = Markdown(**kwargs)
    391     return md.convert(text)
    392 

~/.virtualenvs/ontology/lib/python3.7/site-packages/markdown/core.py in __init__(self, **kwargs)
     98         self.htmlStash = util.HtmlStash()
     99         self.registerExtensions(extensions=kwargs.get('extensions', []),
--> 100                                 configs=kwargs.get('extension_configs', {}))
    101         self.set_output_format(kwargs.get('output_format', 'xhtml'))
    102         self.reset()

~/.virtualenvs/ontology/lib/python3.7/site-packages/markdown/core.py in registerExtensions(self, extensions, configs)
    124         for ext in extensions:
    125             if isinstance(ext, util.string_type):
--> 126                 ext = self.build_extension(ext, configs.get(ext, {}))
    127             if isinstance(ext, Extension):
    128                 ext._extendMarkdown(self)

~/.virtualenvs/ontology/lib/python3.7/site-packages/markdown/core.py in build_extension(self, ext_name, configs)
    164 
    165         try:
--> 166             module = importlib.import_module(ext_name)
    167             logger.debug(
    168                 'Successfuly imported extension module "%s".' % ext_name

~/.virtualenvs/ontology/lib/python3.7/importlib/__init__.py in import_module(name, package)
    125                 break
    126             level += 1
--> 127     return _bootstrap._gcd_import(name[level:], package, level)
    128 
    129 

~/.virtualenvs/ontology/lib/python3.7/importlib/_bootstrap.py in _gcd_import(name, package, level)

~/.virtualenvs/ontology/lib/python3.7/importlib/_bootstrap.py in _find_and_load(name, import_)

~/.virtualenvs/ontology/lib/python3.7/importlib/_bootstrap.py in _find_and_load_unlocked(name, import_)

ModuleNotFoundError: No module named 'outline'

However, md.markdown(s, extensions=['mdx_outline',] seems to work just fine.

This is with Markdown==3.0.1 and python 3.7.2