# HF-20210515

The May 2021 protocol upgrade was the first to be comprised of [CHIPs](#chips).

## CHIPs

A CasH Improvement Proposal (CHIP) is a change request for the BitcoinCash protocol.
CHIPs can be written and published by any member of the BitcoinCash community.
They are evaluated publicly, giving the authors an opportunity to make any clarifications or adjustments based on feedback from the rest of the community.
Once there is sufficient support for a CHIP amongst node developers, it is scheduled for release in a future protocol upgrade.
Changes from multiple CHIPs may be included in a single protocol upgrade.

## Contents

The May 2021 protocol upgrade is comprised the following CHIPs:

1. [Unconfirmed Transaction Chain Limit](/protocol/forks/chips/2021-05-unconfirmed-transaction-chain-limit)
2. [Multiple OP_RETURNs for Bitcoin Cash](/protocol/forks/chips/2021-05-multiple-op-returns-for-bitcoin-cash)