Prior soft forks were activated via miner signaling in block version numbers. Now that the chain has long since passed the blocks at which those consensus rules have triggered, they can be replaced by caching the block heights at which those consensus rules became enforced. This change is a minor one, but it was worth documenting the rationale for posterity. Eric Voskuil points out that this sort of statement represents one consequence of the bad precedent. He asks if checkpoints are good now, if hard forks are okay now, what is the maximum depth of a reorg allowed by this non-machine consensus, and shouldn't we just define a max depth so that all cruft deeper than that can just be discarded on a regular basis? He also questions why there are activation heights defined by this hard fork if it's not possible to reorg back to them. He explains that the "BIP" is neither a Proposal nor an Improvement nor Bitcoin.