every rule should have a default action

element_matching.c

MatchRule register_rule (MatchRule *rule, int type, gchar *name, (void *action)(void))
{
  MatchRule new_rule;
  MatchRule *next = rule;
  
  new_rule.type = type;
  new_rule->name = name;
  new_rule->action = action;
  new_rule->subrule = NULL;
  new_rule->fails = NULL;
  
  while (next) {
    rule = rule->fails;
    next = rule->fails;
  }
  
  if (rule)
    rule->fails = new_rule;
  
  return new_rule;
}