At the moment, we have meta-parameters that you can pass into a request. The ones we have currently:

• _jsonp
• _embed
• _method
• _envelope (Add ability to wrap response in an envelope #628)

We have a finite space to pack these into (query strings). They should never conflict with endpoint arguments in core, but could possibly do so in plugins registering their own. If we stick with the current method, it needs to be documented that these exist and mean something outside the endpoint.