FcPatternAdd man page
FcPatternAdd — Add a value to a pattern
#include <fontconfig/fontconfig.h> FcBool FcPatternAdd (FcPattern *p, const char *object, FcValue value, FcBool append);
Adds a single value to the list of values associated with the property named `object. If `append is FcTrue, the value is added at the end of any existing list, otherwise it is inserted at the beginning. `value' is saved (with FcValueSave) when inserted into the pattern so that the library retains no reference to any application-supplied data structure.