Right now, when building a source map, you can only get a map or a JSON string. When parsing the map, though, you get an instance of the Mapping interface, which provides a few APIs for inspecting the contents but no way to re-serialize the map.

It would be preferable to have a single class representing a source map that can be serialized and inspected. It would also be good to have a more thorough inspection API than Mapping currently provides -- at the very least a way to get a list of all the segments in the source map, a way to access/modify the source files, etc.