[streams] How generic is pipeTo? (#407)

It is said in https://streams.spec.whatwg.org/#rs-pipe-to that pipeTo can be applied generically to other objects than ReadableStream.
It is not clear though whether pipeTo accepts WritableStream objects only or other objects as well.
I guess it is the latter but would the spec be able to state it clearly like done for ReadableStream?

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/streams/issues/407