I created this in an attempt to learn more about Doctrine Extensions, so I could better assist in maintaining the existing package.
There is no metadata parsing yet (e.g. annotations), but metadata is stored in a central Registry for retrieval later. This might be more cumbersome than we want, as you'd need to pass it through to extension listeners so they can retrieve the appropriate metadata.
One thing I do like is that parsed metadata are first-class objects. See TimestampableMetadata.
See the bootstrap file for how the extensions are hooked into Doctrine. From there, classes are well-commented for context.