When I run `arc help land` at rARC1b4a3e0c5eb9, the information it provides about what branch it will land onto by default seems to say that it will land onto `master` unless otherwise specified:
> Land an accepted change (currently sitting in local feature branch __branch__) onto master and push it to the remote.
…
> __--onto__ __master__
> Land feature branch onto a branch other than the default ('master' in git, 'default' in hg). You can change the default by setting 'arc.land.onto.default' with `arc set-config` or for the entire project in .arcconfig.
If I understand the change introduced for {T5690}, however, `arc land` will actually default to landing in the tracking branch, if there is one. If that behavior hasn't since been changed, I think it'd be nice to mention it in the help text, so that people know that they don't have to explicitly specify __--onto__ when they want to land their change in the tracked branch.