[Fontconfig] Expression and Boolean Examples?

[Infinality]

(apologies if this is a duplicate email)

Can someone point me in the direction of some (preferably rich) examples 
that use these elements?

<or>, <and>, <plus>, <minus>, <times>, <divide>
<eq>, <not_eq>, <less>, <less_eq>, <more>, <more_eq>
<not>
<if>

I've done some online searching, but as you can imagine, searching for 
things like "<if>" and "<or>" does not produce the most high-quality 
results.  ;)

Thanks,
Erik