XProc

XProc is an XML transformation language for processing documents in pipelines: chaining conversions and other steps together to achieve the desired results. It can handle documents in XML, HTML, JSON, text and binary.

The current (stable) version is 3.0.^[1] While XProc 1.0^[2] is a W3C Recommendation, XProc 3.0 is a standard developed by the W3C XProc Next Community Group.^[3]

Its main characteristics are:

• XProc is a programming language, expressed in XML, in which you can write pipelines.
• An XProc pipeline takes data as its input (often XML) and passes this through specialized steps to produce end results.
• Steps range from simple ones, like adding attributes, to more complex stuff like splitting/combining/pruning, transformations with XSLT and XQuery, validations against schemas, etc.
• Within a pipeline you can do things like working with variables, branching, looping, catch errors, etc. Everything is based on the data flowing through.
• XProc pipelines are not limited to a linear succession of steps. They can fork and merge.
• XProc allows you to create custom steps by combining other steps. These custom steps can be used just like any other. Therefore, pipelines and steps are interchangeable concepts in XProc.
• Custom steps can be collected into libraries.
• XProc aids in the housekeeping surrounding the processing, like inspecting directories, reading documents from zip files, writing things to disk, etc
• There is software that can execute these pipelines, the so-called XProc processors.