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Chapter 3. Steps and Connections

Steps perform units of work. How those steps are connected together determines the overall result of a pipeline. As we said in Chapter 2, Pipeline Terminology, connections in XProc are always written from the perspective of the step with the input port.

Inputs can be connected in four different ways. An input can be connected to:

  1. A document identified by a URI. “Read from http://example.com/document.xml.”

  2. Another port in the pipeline. “Read the output of the result port on that p:xslt step.”

  3. A literal document specified inline in the pipeline. “Take this hunk of XML from the pipeline document, create a document out of it, and take it as the input.”

  4. An explicitly empty sequence. “Read nothing.”

If an input port accepts a sequence of documents, then more than one input can be specified and the various kinds of connection can be arbitrarily mixed.

If an input port has no explicit connections, then it will automatically be connected to the default readable port, if there is one.

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FIXME: talk about what select on p:input means == separate documents