Geek Thoughts: reading XProc code

All the input/output/port stuff in XProc seemed incomprehensible to me until I recognized something simple. Every time you see a <pipe> element, read it as “comes from”. For example

  <p:output port="result">
    <p:pipe step="validated" port="result"/>
  </p:output>
reads as ‘output to the “result” port comes from the port “result” on step “validated”‘ and
  <p:input port="source">
    <p:pipe step="included" port="result"/>
  </p:input>
reads as ‘input for the “source” port comes from the port “result” on step “included”‘. If you keep this in mind it all makes much more sense.
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