There was a PR in the 3.1 alpha branch (#441) that never had it's sources merged into the 3.1 non-alpha branch(s) but the documentation was still committed here:

d7c8345#diff-58f184d7415a8c22e56e4908527cfd1c7c28ea1c5720cf4280b2d511b25f7409

It lists several runtime options around a boot proc, per-user LRU cache and other things that were never released. Might be a bit tricky trying to re-integrate that PR -- better to probably just remove the documentation.