FcConfigSubstituteWithPat - Execute substitutions
#include <fontconfig/fontconfig.h>
FcBool FcConfigSubstituteWithPat (FcConfig *config, FcPattern *p, FcPattern *p_pat, FcMatchKind kind);
Performs the sequence of pattern modification operations, if kind is
  FcMatchPattern, then those tagged as pattern operations are applied, else if
  kind is FcMatchFont, those tagged as font operations are applied and
  p_pat is used for <test> elements with target=pattern. Returns FcFalse
  if the substitution cannot be performed (due to allocation failure). Otherwise
  returns FcTrue. If config is NULL, the current configuration is used.