A scenario is presented to illustrate how transactions are processed differently by nodes with varying configurations and feature support. For instance, Node X, equipped to handle Taproot and some annex features, with a 300MB mempool and a 10sat/vb minimum fee, interacts differently with transactions than Node Y, which only supports Taproot, has a larger mempool of 1GB, and a lower minimum fee of 5sat/vb.

The example focuses on two transactions: Transaction P, a standard Taproot transaction with a fee rate of 6sat/vb, and Transaction C, which utilizes a new annex feature when spending from Transaction P and carries a higher fee rate of 20sat/vb. Node X accepts both transactions because Transaction C, with its higher fee rate, acts as a Child Pays for Parent (CPFP) transaction, incentivizing the node to include both in its mempool and potentially relay them together. However, Node Y rejects Transaction C due to its inability to validate the annex feature utilized by the transaction, demonstrating how nodes' support for specific features influences transaction propagation.

The decision-making process of whether to relay transactions involves sorting transactions by depth/ancestor count and then by fee rate. This ensures that higher-fee transactions that depend on other transactions (like Transaction C depending on Transaction P) are prioritized for relay. The example further explores how these transactions would be treated by another hypothetical Node Z, running the same software and parameters as Node X, showcasing how transactions might be accepted or rejected based on each node's configuration and the transactions' characteristics.

This nuanced approach to transaction relay underscores the importance of node configuration, feature support, and fee rates in the broader context of cryptocurrency networks. It highlights how changes like softforks, which introduce new features, can have significant implications for transaction propagation and acceptance across the network.