That (define macros, include file that uses them) is fairly vanilla usage of the C preprocessor. Abuse is something like this: <a href="https:&#x2F;&#x2F;github.com&#x2F;rofl0r&#x2F;chaos-pp" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;rofl0r&#x2F;chaos-pp</a> and <a href="https:&#x2F;&#x2F;github.com&#x2F;rofl0r&#x2F;order-pp" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;rofl0r&#x2F;order-pp</a>