http://www.w3.org/ns/xproc (recommended prefix: p)
The main XProc namespace, used for all of its elements, steps and some of its attributes.
http://www.w3.org/ns/xproc-step (recommended prefix: c)
This namespace is used for documents that are inputs or outputs from several standard and optional steps.
http://www.w3.org/ns/xproc-error (recommended prefix: err)
This namespace is used for XProc errors.
http://www.w3.org/2001/XMLSchema (recommended prefix: xs)
This namespace is used for data types, such as xs:string and xs:boolean.
http://www.w3.org/ns/xproc-http (recommended prefix: rh)
The namespace used for specifying request headers in document-properties in the p:http-request step.