This file is indexed.

/usr/share/xscreensaver/config/penrose.xml is in xscreensaver-data 5.36-1ubuntu1.

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The actual contents of the file can be viewed below.

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<?xml version="1.0" encoding="ISO-8859-1"?>

<screensaver name="penrose" _label="Penrose">

  <command arg="-root"/>

  <video href="https://www.youtube.com/watch?v=atlkrWkbYHk"/>

   <hgroup>
    <vgroup>
     <number id="delay" type="slider" arg="-delay %"
             _label="Frame rate" _low-label="Low" _high-label="High"
             low="0" high="100000" default="10000"
             convert="invert"/>

     <number id="ncolors" type="slider" arg="-ncolors %"
               _label="Number of colors" _low-label="Two" _high-label="Many"
               low="1" high="255" default="64"/>
    </vgroup>
    <vgroup>
     <number id="size" type="slider" arg="-size %"
              _label="Tile size" _low-label="Small" _high-label="Large"
              low="1" high="100" default="40"/>

     <boolean id="ammann" _label="Draw ammann lines" arg-set="-ammann"/>
     <boolean id="showfps" _label="Show frame rate" arg-set="-fps"/>
    </vgroup>
   </hgroup>
  

  <xscreensaver-updater />

  <_description>
Quasiperiodic tilings.

In April 1997, Sir Roger Penrose, a British math professor who has
worked with Stephen Hawking on such topics as relativity, black
holes, and whether time has a beginning, filed a
copyright-infringement lawsuit against the Kimberly-Clark
Corporation, which Penrose said copied a pattern he created (a
pattern demonstrating that "a nonrepeating pattern could exist in
nature") for its Kleenex quilted toilet paper.  Penrose said he
doesn't like litigation but, "When it comes to the population of
Great Britain being invited by a multinational to wipe their bottoms
on what appears to be the work of a Knight of the Realm, then a last
stand must be taken."

As reported by News of the Weird #491, 4-Jul-1997.

https://en.wikipedia.org/wiki/Penrose_tiling
https://en.wikipedia.org/wiki/Tessellation

Written by Timo Korvola; 1997.
  </_description>
</screensaver>