What specifically is Amazon Redshift patch 178 changing for DECODE?

In the cluster patch notes for path 178 https://docs.aws.amazon.com/redshift/latest/mgmt/cluster-versions.html:

The DECODE function replaces a specific value with either another specific value or a default value, depending on the result of an equality condition. DECODE now requires the following three parameters:

• expression
• search
• result

The DECODE function already exists and was documented, what exactly is it that's changing vs the previous version?