code: def implicit_includes (self, feature, target_type):
          
          assert isinstance(feature, basestring)
          assert isinstance(target_type, basestring)
          if not target_type:
              key = feature
          else:
              key = feature + "-" + target_type
  
  
          result = self.implicit_includes_cache_.get(key)
          if not result:
              target_paths = self.all_target_directories(target_type)
              target_paths = unique(target_paths)
              result = ["<%s>%s" % (feature, p) for p in target_paths]
              self.implicit_includes_cache_[key] = result
  
          return result
docs: Returns the properties which specify implicit include paths to
              generated headers. This traverses all targets in this subvariant,
              and subvariants referred by <implcit-dependecy>properties.
              For all targets which are of type 'target-type' (or for all targets,
              if 'target_type' is not specified), the result will contain
              <$(feature)>path-to-that-target.