The email parser class returns the wrong type for the parsed message

Summary

According to the documentation,

The email package provides a standard parser that understands most email document structures, including MIME documents. You can pass the parser a bytes, string or file object, and the parser will return to you the root EmailMessage instance of the object structure.

In fact, the parser returns an object of the legacy Message class. Code which takes the documentation at face value will blow up if it attempts to invoke methods which the newer class has but the older class does not.

Environment

Python 3.11.1 (v3.11.1:a7a450f84a, Dec 6 2022, 15:24:06) [Clang 13.0.0 (clang-1300.0.29.30)] on darwin

Repro

Here is a small program which demonstrates the problem.

Code

#!/usr/bin/env python3

import email

message_bytes = (
    b'Content-type: multipart/form-data; boundary=------abracadabra\r\n'
    b'\r\n'
    b'------abracadabra\r\n'
    b'Content-Disposition: form-data; name="f"; filename="f1"\r\n'
    b'Content-Type: application/octet-stream\r\n'
    b'\r\n'
    b'\x01\r\n'
    b'------abracadabra--\r\n'
)

message = email.message_from_bytes(message_bytes)
print(f'type of message is {type(message)}')
print('have get_content()?', hasattr(message, 'get_content'))

Output

% ./email-message-repro.py
type of message is <class 'email.message.Message'>
have get_content()? False

Run the supplied reproducer and inspect the email.message_from_bytes entry point, along with the linked parser and EmailMessage documentation. Determine whether the intended fix is to change the returned type or correct the documentation, then add coverage for the demonstrated behavior and verify the documented API and runtime result agree.