Pipelines consist of a list of Stages. The purpose of a Pipeline is to produce or modify an XRD. Each Stage on the Pipeline can modify the XRD. The CREATE Pipeline is executed every time a new XRI subsegment with a new XRI authority is created. The Pipeline "initializes" the XRD of the new authority. The LOOKUP Pipeline is executed every time an external resolution request is processed. It is used for "dynamically adjusting" an XRD for a particular request (e.g. setting an <Expires> tag).