Standardize extension to content type mapping?

(This discussion could go here or HTML — which notes "Extensions tend to be ambiguous..." — but I'm guessing the right eyeballs will be here.)

When a File is minted via a drop operation or HTMLInputElement in Chrome, the content type is determined using platform-specific logic. e.g. on Windows the registry is used as is normal for the platform. There's also a small fallback list built into the browser. This causes behavior to differ for the same version of Chrome on the same OS depending on what applications are installed (e.g. .DOCX may be unknown if Office is not installed). Presumably this is also an interop issue across browsers on the same machine if different logic/lists are used is used.

Web applications should trust neither extensions nor content types. But should we attempt to standardize the behavior here in any way, e.g. an expected list of extension → type mappings, to avoid developer surprise?

I'm not strongly advocating for this, just wanted to kick off the discussion.

Beginne mit dem Issue zu File API und dem referenzierten Verhalten von HTMLInputElement. Vergleiche die für Chrome beschriebene plattformspezifische Zuordnung von Erweiterungen zu Content-Types mit den bestehenden Anmerkungen zu File API und HTML. Als erledigt würde eine geklärte Spezifikationsrichtung gelten, etwa die Entscheidung, ob eine standardisierte Zuordnung erforderlich ist, und die Definition ihres Umfangs.