The premise revolves around how to prioritize addresses when a URI includes both traditional and more modern or custom address types. Specifically, there's contemplation over a scenario where a Bitcoin URI might include multiple addresses with different parameters, leading to questions about which address should be given precedence.

A proposed structure suggests listing addresses in a manner that inherently prioritizes newer or more specialized addresses over older, more universally compatible ones. This is exemplified by suggesting an order where address1 is placed last due to its nature as the most backward-compatible and presumably least desirable option compared to address2 and address3. This setup implies a preference hierarchy based on the modernity and specific utility of each address type.

Additionally, the conversation touches upon the challenges of integrating both on-chain and off-chain addresses within the same URI. It raises concerns about how to clearly signify the priority of an off-chain address (denoted as b12_address) when mixed with traditional on-chain addresses. The possibility of introducing order dependence at the URI level is mentioned as a potential solution, though it acknowledges the complexity this adds.

The overarching theme is the need for a methodical approach to determine the order of preference among various Bitcoin addresses within a URI. This includes balancing the desire to embrace newer address formats with the necessity of maintaining backward compatibility. The dialogue suggests an ongoing exploration of how best to update BIP21 to address these priorities effectively, hinting at the broader implications for users and systems interacting with Bitcoin URIs.