XProc optional steps in Componize

Componize implements the optional p:exec and p:xsl-formatter steps to allow external commands and XSL-FO processing.

p:exec
Runs an external command passing the input that arrives on its source port as standard input, reading result from standard output, and errors from standard error.
p:xsl-formatter
Receives an XSL 1.1 document and renders the content. The result of rendering is stored to the URI provided via the href option. A reference to that result is produced on the output port.