XSL-FO nodes have a single input port that you use to specify the XML to be converted to PDF. This node expects XML defined using the FO grammar. You can specify a default value, or the value can be dynamic (the output from another node in the XML pipeline, for example). XSL-FO nodes are typically piped to XQuery and XSLT nodes, but they can be piped to any node that outputs XML using the FO grammar.