Font aliasing in linux (ie for Helvetica)

31-my-font-aliases.conf

<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<!-- 
On void, see /etc/fonts/conf.d/30-metric-aliases.conf
Sets the google font Arimo for sans-serif, and adds an alias for Helvetica 
-->
<fontconfig>
  <alias>
    <family>sans-serif</family>
    <prefer><family>Arimo</family></prefer>
  </alias>
  <match>
    <test name="family"><string>Arial</string></test>
    <edit name="family" mode="assign" binding="strong">
      <string>Arimo</string>
    </edit>
  </match>
  <match>
    <test name="family"><string>Helvetica</string></test>
    <edit name="family" mode="assign" binding="strong">
      <string>Arimo</string>
    </edit>
  </match>
</fontconfig>