Define custom content type for Page Template (fixes #1212)

[dataflake]

Fixes #1212

I chose to put the mime.types file into the PageTemplates product itself because I didn't see a sensible place elsewhere where I can load it during initialization.

[d-maurer]

In view of https://www.rfc-editor.org/rfc/rfc2046#section-6 we likely should start our subtype with X- (indicating a somewhat unofficial value).
Because a page template is mostly human readable, text might be better than application as top level type.
However, because we only plan to use the type internally (and not for publication), the precise value is not of great importance.

We might also check that the appearance of a ".pt -> MIME type" map in public registries does not pose a problem on a different route: browsers may consult those registries to automatically provide a "Content-Type" header which might prevent our guessing. However, if this really happens, I have no idea how to prevent it (the browser's info may be authoritative and not based on guessing).

[d-maurer]

Alternatively, we could apply the same logic as for .dtml, e.g. use

elif ext in ('.pt', '.zpt') or typ in (...

[mauritsvanrees]

Relying on the extension might indeed be better.

Otherwise I wonder what happens when the operating system associates .pt with that other mime type you found. Does the new Zope definition win? Does the OS definition win? Does it matter on the order in which the two definitions get loaded?

[d-maurer]

Maurits van Rees wrote at 2024-5-17 12:32 -0700:

... Relying on the extension might indeed be better. Otherwise I wonder what happens when the operating system associates `.pt` with that other mime type you found. Does the new Zope definition win?

All depends on Python's `mimetypes` module. This promises that later registered type files take precedence over former ones. The first type files registered are those provided by the system. Thus, the Zope definition will win unless the application registers additional files with conflicting definitions.

Does the OS definition win? Does it matter on the order in which the two definitions get loaded?

In principle, yes: but the system provided files are registered before any others.

[dataflake]

I chose the simplest possible solution.