the idea is that often times in code, you will see something like this:...

src/factory.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 86 matching lines @@
 
   // Allocates and partially initializes a TwoByte String. The characters of
   // the string are uninitialized. Currently used in regexp code only, where
   // they are pretenured.
   static Handle<String> NewRawTwoByteString(
       int length,
       PretenureFlag pretenure = NOT_TENURED);
 
   // Create a new cons string object which consists of a pair of strings.
   static Handle<String> NewConsString(Handle<String> first,
-                                      Handle<String> second);
+                                      Handle<String> second,
+                                      PretenureFlag pretenure = NOT_TENURED);
 
   // Create a new sliced string object which represents a substring of a
   // backing string.
   static Handle<String> NewStringSlice(Handle<String> str,
                                        int begin,
                                        int end);
 
   // Creates a new external String object.  There are two String encodings
   // in the system: ASCII and two byte.  Unlike other String types, it does
   // not make sense to have a UTF-8 factory function for external strings,
@@ skipping 259 matching lines @@
   // Update the map cache in the global context with (keys, map)
   static Handle<MapCache> AddToMapCache(Handle<Context> context,
                                         Handle<FixedArray> keys,
                                         Handle<Map> map);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_