#include <fontconfig.h>
FcBool FcPatternAddWeak(FcPattern *p, const char *object, FcValue value, FcBool append);
FcBool FcPatternAddWeak
FcPatternAddWeak is essentially the same as FcPatternAdd except that any values added to the list have binding weak instead of strong.
Fontconfig version 2.8.0