Since we don't know what sort of address changes will happen later on, you could make this future-proof by passing a list of addresses to `addr`.

The syntax is

bitcoin:<address>[?addr=<address>[,<address>[,<address>]]]

The addresses passed as a comma-separated list to the `addr` parameter are in descending order of preference, with highest first. A consumer of this URI should attempt to understand each address in the list before falling back to the next address and finally to the base address after `bitcoin:`.

Example:

bitcoin:3xBase58compatibleAddress?addr=fancyFutureEncoding0x01,bech32address1qx01

The spending wallet would attempt to spend to "fancyFutureEncoding0x01" then to "bech32address1qx01" and finally to "3xBase58compatibleAddress".

Thanks,

-Clark


On Sun, Oct 14, 2018 at 3:14 PM Srintuar via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

An extremely simple BIP write-up for a backward compatible URI scheme to help with segwit adoption by online stores and merchants.



====

This BIP is a modification of an earlier [[bip-0021.mediawiki|BIP 0021]] by Nils Schneider and Matt Corallo

==Abstract==
This BIP proposes a URI scheme which allows for backward compatibility with native segwit (bech32) wallets and legcy wallets (base58)

==Motivation==
The purpose of this URI scheme is to enable all users to easily make payments from any wallet, without allowing backward compatibility to be a barrier to segwit adoption. This BIP allows a merchant to preferentially receive payments to a bech32 address, while gracefully allowing older clients to make base58 encoded payments.

==Specification==

=== Query Keys ===

*addr: an alternative bitcoin destination which is preferred over the "bitcoinaddress" field of the url

== Appendix ==

=== Simpler syntax ===

 <nowiki>bitcoin:<address>[?amount=<amount>][?label=<label>][?message=<message>][?addr=<bech32address>]</nowiki>

=== Examples ===

Just the address:
 bitcoin:3BnsWZiTdYVrqiPh2RP3q9Y3ZqvhbCN2it?addr=bc1q5u92yq20hss4rc99mfu23h4dxkxn4uuyqd5dzy&amount=50&label=Luke-Jr&message=Donation%20for%20project%20xyz


== Reference Implementations ==
=== Bitcoin clients ===

* none yet

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