Gordon P. Hemsley

Chromium has been using the string `"Rar!\x1A\x07\x00"` since its initial commit in 2008, so I think this may have been a mistake in converting to bytes for the original draft...

A ZIP-based MIME type is one that is based off of the ZIP file format; that means things like JAR, XML-based Microsoft Office files, XPI, etc. I think perhaps you...

As I recall, I kept that name solely because it was linked to from somewhere else (probably HTML), if that helps. I didn't care for it, either.

Firefox is: https://hg.mozilla.org/mozilla-central/file/tip/dom/media/ADTSDemuxer.cpp

I don't think we want to be sniffing the CR3 format specifically, either positively or negatively. However, [a later comment](https://bugzilla.mozilla.org/show_bug.cgi?id=1725190#c5) in the linked bug indicates that Firefox is using the...

(No separate issue, so commenting here.) Chromium treats `""`, `"unknown/unknown"`, `"application/unknown"`, and `"*/*"` as unknown MIME types: https://chromium.googlesource.com/chromium/src.git/+/refs/heads/main/net/base/mime_sniffer.cc Firefox defines `UNKNOWN_CONTENT_TYPE` as `"application/x-unknown-content-type"` and `APPLICATION_GUESS_FROM_EXT` as `"application/x-vnd.mozilla.guess-from-ext"`: https://hg.mozilla.org/mozilla-central/file/tip/netwerk/mime/nsMimeTypes.h But also...

With a payload of `

Support for `application/unknown` and `unknown/unknown` were [reported to be](https://www.adambarth.com/papers/2009/barth-caballero-song.pdf) exclusive to Chrome as of May 2009. (Internet Explorer 7, Firefox 3, and Safari 3.1 did not support them.)

https://www.w3.org/Bugs/Public/show_bug.cgi?id=20003 is also concerned about the scope of which contexts the spec applies to. (There is some concern about sniffing resources on the filesystem, for example.)

Note that mention of X-Content-Type-Options was removed in 64bfe025012be3ded16ac4978844acc0e8dfec3c because "it's [defined by Fetch](https://fetch.spec.whatwg.org/#x-content-type-options-header)" and that the [no-sniff flag](https://mimesniff.spec.whatwg.org/#no-sniff-flag) in mimesniff is set according to its value.