celestia/x-celestia-script.xml

<?xml version="1.0"?>
<mime-info xmlns='http://www.freedesktop.org/standards/shared-mime-info'>
  <mime-type type="application/x-celestia-script">
    <sub-class-of type="text/plain"/>
    <generic-icon name="celestia"/>
    <comment>Celestia script file</comment>
    <glob pattern="*.cel"/>
    <glob pattern="*.celx"/>
  </mime-type>
</mime-info>