Json response and rate limits

[Gui]

Hello,

1/

Is there a way to get a json response (instead of xml) ?

I'm trying with get_slideshows_by_user endpoint :

- adding parameter "format=json" : no effect

- request headers content-type and/or accept : no effect

The documentation is showing some responses with either json/xml format, but there is no explaination about how to get the "json" one.

2/

get_slideshows_by_user 

=> what is the rate limit for calling that endpoint ? and others ?

Thanks.