.fonts.conf

<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
    <dir>/usr/share/fonts</dir>
    <dir>~/.fonts</dir>

    <alias>
        <family>Open Sans</family>
        <default><family>serif</family></default>
    </alias>

    <match target="pattern">
        <test name="family"><string>serif</string></test>
        <edit name="family" mode="append"><string>Open Sans</string></edit>
    </match>

    <alias>
        <family>Open Sans</family>
        <default><family>sans-serif</family></default>
    </alias>

    <match target="pattern">
        <test name="family"><string>sans-serif</string></test>
        <edit name="family" mode="append"><string>Open Sans</string></edit>
    </match>

    <alias>
        <family>Open Sans</family>
        <default><family>sans</family></default>
    </alias>

    <match target="pattern">
        <test name="family"><string>sans</string></test>
        <edit name="family" mode="append"><string>Open Sans</string></edit>
    </match>

    <alias>
        <family>SF Mono</family>
        <default><family>monospace</family></default>
    </alias>

    <match target="pattern">
        <test name="family"><string>monospace</string></test>
        <edit name="family" mode="append"><string>SF Mono</string></edit>
    </match>

</fontconfig>