Update doc as well.

include/v8.h

 // Copyright 2007-2009 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 837 matching lines @@
    * the contents of the string and the NULL terminator into the
    * buffer.
    *
    * Copies up to length characters into the output buffer.
    * Only null-terminates if there is enough space in the buffer.
    *
    * \param buffer The buffer into which the string will be copied.
    * \param start The starting position within the string at which
    * copying begins.
    * \param length The number of bytes to copy from the string.
-   * \param nchars The number of characters written.
+   * \param nchars_ref The number of characters written, can be NULL.
    * \return The number of bytes copied to the buffer
    * excluding the NULL terminator.
    */
   int Write(uint16_t* buffer, int start = 0, int length = -1) const;  // UTF-16
   int WriteAscii(char* buffer, int start = 0, int length = -1) const;  // ASCII
   int WriteUtf8(char* buffer,
                 int length = -1,
                 int* nchars_ref = NULL) const; // UTF-8
 
   /**
@@ skipping 2523 matching lines @@
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef V8EXPORT_INLINE
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_