Documentation

The current (unregistered) IANA Media Type types for Python (text\/x-python.*):

1. ``text/x-python`` instead of ``text/plain``.

   ¹

2. <Extension Id="py" ContentType="text/x-python">

   ²

3. 	'.pyc' : 'application/x-python-code',
   	'.pyo' : 'application/x-python-code',

   ³

...appear to be incorrect, per current guidance, for RFC 6838 states that the x- prefix has been deprecated in favour of the x. tree: ⁴

The unregistered tree includes media types intended exclusively for use in private environments and only with the active agreement of the parties exchanging them. It uses the x. tree prefix. Examples are application/x.foo, video/x.bar. Media types in this tree cannot be registered.

This type was originally defined in RFC 1590 (published in September 1993) using the x- or X- prefix. RFC 2048 (published in November 1996) introduced the x. prefix, but discouraged use of the unregistered tree, as new personal and vendor trees with relaxed registration requirements are now available. The current RFC 6838 (published in January 2013) maintains the same recommendation, but subtypes prefixed with x- or X- are no longer considered to be members of this tree.

Media types that have been widely deployed (with a subtype prefixed with x- or X-) without being registered, should be, if possible, re-registered with a proper prefixed subtype.

Footnotes

1. 49d72365cd2d6c09a154a9a061efef4130e2c758/Misc/NEWS.d/3.10.0a1.rst?plain=1#L3030C1-L3030C44 ↩

2. 49d72365cd2d6c09a154a9a061efef4130e2c758/Tools/msi/launcher/launcher_reg.wxs#L9C32-L9C67 ↩

3. 49d72365cd2d6c09a154a9a061efef4130e2c758/Lib/mimetypes.py#L540C9-L541C48 ↩

4. en.wikipedia.org/w/index.php?title=Media_type&oldid=1292890008#Unregistered_tree ⁵ ↩

5. serialseb..com/issues/24#issue-3136552984 ↩

I don't think we should change mimetypes.py. Even if it's deprecated, it's still common practice and I think "practicality beats purity" here.

Now, using x. means that we're using the "unregistered tree" and it's still discouraged:

RFC 2048 (published in November 1996) introduced the x. prefix, but discouraged use of the unregistered tree, as new personal and vendor trees with relaxed registration requirements are now available. The current RFC 6838 (published in January 2013) maintains the same recommendation

I would be for the status quo in this case. Strictly speaking, we can use x-* Mime types even though they don't belong to the unrgistered tree. Note that there are some x-* in the official Media Types (look for /x- in https://www.iana.org/assignments/media-types/media-types.xhtml).