<dfn>system exclusive</dfn> are defined in [[MIDI]].

devices, particularly if system exclusive access is requested. In

some scenarios, this permission may have already been implicitly

or explicitly granted, in which case this prompt may not appear.

If the user gives express permission or the call is otherwise

approved, the vended Promise is resolved. The underlying system

may choose to allow the user to select specific MIDI interfaces

to expose to this API (i.e. pick and choose interfaces on an

individual basis), although this is not required. The system may

also choose to prompt (or not) based on whether system exclusive

support is requested, as system exclusive access has greater

privacy and security implications.

devices. This prompt may be contingent upon whether system

exclusive support was requested, and may allow the user to

receive system exclusive messages is requested or allowed on a

given {{MIDIAccess}} object. On the option passed to

system exclusive support is denied (either by policy or by user

action), the access request will fail with a {{"SecurityError"}}

error. If this support is not requested (and allowed), the system

will throw exceptions if the user tries to send system exclusive

messages, and will silently mask out any system exclusive

messages received on the port.

This attribute informs the user whether system exclusive support is

enabled on this MIDIAccess.

If the {{MIDIAccess}} did not enable system exclusive access,

and the message is a system exclusive message, abort this

process.

If <var>data</var> is a system exclusive message, and the

{{MIDIAccess}} did not enable system exclusive access, throw an

<code>InvalidAccessError</code> exception.

Requesting Access to the MIDI System with System Exclusive Support

including the ability to send and receive system exclusive

This example loops all input messages on the first input port to

the first output port - including system exclusive messages.

available, and then use it to download data - e.g. samples stored in

a sampler - or replace that data (erasing sample data or patches in

the device), although both these scenarios would have to be coded for

a particular device. It is also possible that some samplers might

enable a system exclusive message to start recording a sample - so if

the sampler happened to have a dedicated microphone attached

(uncommon in practice, but possible), it would be possible to write

code specific to a particular device that could record a short sample

of sound and then upload it to the network without further user

(although again, this requires much device-specific code; there is

not standardized “grab all patches and hash it” capability.) This

does suggest that system exclusive messages are in a security

Unfortunately, some common MIDI commands are also sent as system

exclusive messages (MIDI Machine Control, for example - generic

start/stop/rew/ffw commands) - and many devices use system exclusive

to program patches, send advanced controller messages, download

firmware, etc., which are much-demanded scenarios for Web MIDI. Some

devices use sysex as a direct control protocol, as they can pack more

data into a single “message”, and most devices use SysEx as way to

save and restore patches and configuration information on

System Exclusive, on the other hand, has a much less bounded

allows user agents to require the user's approval before giving

access to MIDI devices, although it is not currently required to

prompt the user for this approval - but it also detailed that system

exclusive support must be requested as part of that request.