Android M Source code Tagging

Okay, I'm trying to build Marshmallow preview 2 for the Nexus 7 2012, and I'm unsure of the source tagging on Google git.
I want to download the files using repo init, but obvious branch names aren't working.

I've tried this:

Code:

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repo init -u https://android.googlesource.com/platform/manifest -b m-preview-1

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But this returns a 404 error.

I think the manifest file is correct, but "m-preview-1" is a tag and not a branch name like last year's "l-preview" branch.

TL;DR
What is the repo init command to download the Nexus 7 2012 Android M preview 2 branch?

P.S
M preview 3 isn't on the git, which is why I'm doing preview 2.