A {@link Locator} which wraps a {@link XMLPipelineContext} and delegates theinterface methods to the current locator set in that context.
The only information that can really be relied upon from this to be correct is the system id, all other are not available in all but the simplest of pipelines. The system id returned from this tracks the base URL for the element and while the base URL and the system id from the context's current locator stay in sync then the information from the locator is returned, otherwise the base URL is returned as the system id and all other methods return the appropriate unavailable value.