However, the set of valid parameters one can pass to these methods
(and their meaning), does not seem to be defined anywhere else
in the document.

This is confusing. Sometimes zip() has an appendix, sometimes it
is removed (ok bad joke, but still !). The manual should say what it is.

Agreed. And if you have a better term then appendix I think we are very happy to change this. At the time I created it I could not come up with something better although I was never that happy with the term.

.bq Also, can jar() take a single string argument, or is this a typo?

We have forgotten to update this. In earlier versions this was possible, not any longer.

As announced on the Gradle blog we are planning to completely migrate issues from JIRA to GitHub.

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Thanks again for reporting this issue. We haven't heard back from you after our inquiry from November 15th. We are closing this issue now. Please create an issue on GitHub if you still feel passionate about getting it resolved.