The Change History lists major changes users need to be aware if upgrading from one version to another. It is a high level summary of selected changes that may impact applications or might even break backwards compatibility. Please, consult the CHANGES file contained in the source distribution for a more complete list of changes. If you are eager to learn about all changes, even smaller ones that do not make it into the CHANGES file, you may want to monitor PECL commit messages. To do you, you could, for example, subscribe to the PECL commit message mailing list.