The new Eventing Service framework in Couchbase Server 6.5 enables writing custom functions to process data change events such as create, update and delete/expiry events. One of the key improvements is the removal of a previous limitation that prevented functions from mutating documents on their source bucket, which now allows for more complex use cases like enriching changed documents with new attributes or performing cascade updates or deletes of dependent documents. The Eventing framework also includes a `curl` function to interact with external systems, and the ability to pause and resume running functions, allowing for mid-flight code changes without disrupting ongoing operations. Additionally, an Eventing function can now identify modifications made in a document by comparing the original and updated versions.