This file is indexed.

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

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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

<screensaver name="substrate" _label="Substrate">

  <command arg="-root"/>

  <video href="https://www.youtube.com/watch?v=dCCVgBOVD0E"/>

  <hgroup>
   <vgroup>
    <number id="speed" type="slider" arg="-growth-delay %"
            _label="Frame rate" _low-label="Low" _high-label="High"
            low="0" high="100000" default="18000" convert="invert"/>

    <number id="maxcyc" type="slider" arg="-max-cycles %"
            _label="Duration"  _low-label="Short" _high-label="Long"
            low="2000" high="25000" default="10000" />

    <number id="sandg" type="slider" arg="-sand-grains %"
            _label="Sand grains" _low-label="Few" _high-label="Lots"
            low="16" high="128" default="64" />

    <number id="curve" type="slider" arg="-circle-percent %"
            _label="Circle percentage" _low-label="0%" _high-label="100%"
            low="0" high="100" default="33" />
   </vgroup>
   <vgroup>
    <number id="init" type="spinbutton" arg="-initial-cracks %"
            _label="Initial cracks" low="3" high="15" default="3"/>

    <boolean id="wire" _label="Wireframe only" arg-set="-wireframe" />

    <boolean id="seamless" _label="Seamless mode" arg-set="-seamless" />

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

  <xscreensaver-updater />

  <_description>
Crystalline lines grow on a computational substrate.  A simple
perpendicular growth rule creates intricate city-like structures.

Written by J. Tarbell and Mike Kershaw; 2004.
  </_description>
</screensaver>