Type Definition webrender_api::PipelineSourceId 
                   
                       [−]
                   
               [src]
type PipelineSourceId = u32;
This type carries no valuable semantics for WR. However, it reflects the fact that
clients (Servo) may generate pipelines by different semi-independent sources.
These pipelines still belong to the same IdNamespace and the same DocumentId.
Having this extra Id field enables them to generate PipelineId without collision.