It still sounds like you're advocating removing the requirement that UAs
support application/octet-stream (which makes sense, since its behaviour
doesn't seem to be specified anyway).

If you're suggesting something else, please elaborate on what that
something else is. :)

On Thu, 25 Jun 2015 at 16:23 Florian Bösch <> wrote:

> No, what I'm saying is that if you restrict mime types (or don't
> explicitly prohibit such restriction), but require
> application/octet-stream, that application/octet-stream becomes the
> "undesirable mime-type" dumping ground. And that would be bad because that
> makes it much harder for applications to deal with content. But if that's
> the only way UAs are going to act, then applications will work around that
> by using elaborate guessing code based on magic bytes, and perhaps some
> application developers will use their own mime-type annotation pretended to
> the octet-stream.
> If you inconvenience people, but don't make it impossible to work around
> the inconvenience, then people will work around the inconvenience. It can't
> be the intention to encourage them work around it. So you've got to either
> not inconvenience them, or make working around impossible.
> On Thu, Jun 25, 2015 at 5:07 PM, Wez <> wrote:
>> Florian, you keep referring to using application/octet-stream - that's
>> not a format that all user agents support (although the spec says they
>> should ;), nor is there any mention in the spec of what it means to place
>> content on the clipboard in that format (given that platform native
>> clipboards each have their own content-type annotations).
>> So it sounds like you're saying we should also remove
>> application/octet-stream as a mandatory format?
>> On Thu, 25 Jun 2015 at 15:55 Florian Bösch <> wrote:
>>> It's very simple. Applications need to know what's in the clipboard to
>>> know what to do with it. There is also a vast variety of things that could
>>> find itself in the clipboard in terms of formats, both formal and informal.
>>> Mime types are one of these things that applications would use to do that.
>>> If a UA where to restict what mime type you can put into the clipboard,
>>> that forces the clipboard user to use application/octet-stream. And in
>>> consequence, that forces any such-willing application to forgoe the
>>> mime-type information from the OS'es clipboard API and figure out what's in
>>> it from the content. In turn this would give rise to another way to markup
>>> mime-types in-line with the content. And once you've forced such ad-hoc
>>> solutions to emerge for meddling with what people can put in the clipboard,
>>> you'll have no standing to put that geenie back in the bottle, again,
>>> relevant XKCD quote omitted.
>>> On Thu, Jun 25, 2015 at 4:48 PM, Wez <> wrote:
>>>> You've mentioned "resorting to application/octet-stream" several times
>>>> in the context of this discussion, where AFAICT the spec actually only
>>>> describes using it as a fall-back for cases of file references on the
>>>> clipboard for which the user agent is unable to determine the file type.
>>>> So IIUC you're suggesting that user agents should implement
>>>> "application/octet-stream" (as is also mandated by the spec, albeit without
>>>> a clear indication of what it means in this context) by putting the content
>>>> on the clipboard as an un-typed file?
>>>> Again, I'm unclear as to what the alternative is that you're proposing?
>>>> On Thu, 25 Jun 2015 at 15:27 Florian Bösch <> wrote:
>>>>> Surely you realize that if the specification where to state to only
>>>>> "safely" expose data to the clipboard, this can only be interpreted to 
>>>>> deny
>>>>> any formats but those a UA can interprete and deem well-formed. If such a
>>>>> thing where to be done, that would leave any user of the clipboard no
>>>>> recourse but to resort to "application/octett-stream" and ignore any other
>>>>> metadata as the merry magic header guessing game gets underway. For all
>>>>> you'd have achieved was to muddle any meaning of the mime-type and forced
>>>>> applications to work around an unenforceable restriction.
>>>>> On Thu, Jun 25, 2015 at 3:21 PM, Wez <> wrote:
>>>>>> And, again, I don't see what that has to do with whether the spec
>>>>>> mandates that user agents let apps place JPEG, PNG or GIF directly on the
>>>>>> local system clipboard. The spec doesn't currently mandate OpenEXR be
>>>>>> supported, so it's currently up to individual user agents to decide 
>>>>>> whether
>>>>>> they can support that format safely.
>>>>>> On Thu, 25 Jun 2015 at 14:16 Florian Bösch <> wrote:
>>>>>>> On Thu, Jun 25, 2015 at 3:13 PM, Wez <> wrote:
>>>>>>>> I think there's obvious value in support for arbitrary
>>>>>>>> content-specific formats, but IMO the spec should at least give 
>>>>>>>> guidance on
>>>>>>>> how to present the capability in a safe way.
>>>>>>> Which is exactly the core of my question. If you intend to make it
>>>>>>> say, safe to put OpenEXR into the clipboard (as opposed to letting an 
>>>>>>> app
>>>>>>> just put any bytes there), the UA has to understand OpenEXR. Since I 
>>>>>>> don't
>>>>>>> see how the UA can understand every conceivable format in existence both
>>>>>>> future and past, I don't see how that should work.

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