Sjors Provoost via bitcoin-dev
2017-12-05 19:24:04 UTC
One way to reduce fees is to encourage usage of Replace-By-Fee, BIP 125 . It allows wallets to recommend lower fees, because if a transaction gets stuck due to underestimation, the fee can easily be bumped.
Bitcoin Core has had support for RBF for a while, and as of v0.15.0 recommends lower fees  when the user chooses to use RBF.
I recently submitted a pull request that would turn on RBF by default, which triggered some discussion . To ease the transition for merchants who are reluctant to see their customers use RBF, Matt Corallo suggested that wallets honor a no125=1 flag.
So a BIP-21 URI would look like this: bitcoin:175t...45W?amount=20.3&no125=1
When this flag is set, wallets should not use RBF, regardless of their default, unless the user explicitly overrides the merchant's preference.
Afaik adding this flag won't break existing BIP-21 support. It doesn't use the req- prefix, because it's optional. I'm also not aware of any ad hoc standards that use no125 in BIP-21-ish URIs.
P.S. I'd similarly suggest adding a bech32 param, but that's for another discussion