On some ancient systems { and } don't exist. So an alternarive made of more common characters is provided. There is also a two-character combination for [ and ] and a three character combination for |, & and some other characters. The feature is called digraphs/trigraphs and is disabled on most modern compilers by default.

> The feature is called digraphs/trigraphs and is disabled on most modern compilers by default.

Digraphs and trigraphs are treated differently. <% and %> are fine on GGC and Clang, but ??< and ??> are disabled by default. Both need the -trigraphs option.

Ah okay I knew about that whole thing, I didn't think C had so many of them.