No, not defined means it's not within the purview of the spec. Spec doesn't care. You can send one. Maybe it'll work, maybe it won't, maybe it'll crash, maybe it'll be rejected, maybe some proxy along the way will strip it and the server won't even get it, maybe it'll get your client banned forever.
All of these are fine, because spec doesn't care.
> If accepting body in GET is out of spec, then spec is supposed to say, GET cannot send body.
No, then it would be against spec, like HEAD with a response body.
No, not defined means it's not within the purview of the spec. Spec doesn't care. You can send one. Maybe it'll work, maybe it won't, maybe it'll crash, maybe it'll be rejected, maybe some proxy along the way will strip it and the server won't even get it, maybe it'll get your client banned forever.
All of these are fine, because spec doesn't care.
> If accepting body in GET is out of spec, then spec is supposed to say, GET cannot send body.
No, then it would be against spec, like HEAD with a response body.