public void append(byte[] b,int off,int len){
  grow(ref.length + len);
  System.arraycopy(b,off,ref.bytes,ref.length,len);
  ref.length+=len;
}

public void append ( byte [ ] b , int off , int len ) { grow ( ref . length + len ) ; System . arraycopy ( b , off , ref . bytes , ref . length , len ) ; ref . length += len ; }
append the provided bytes to this builder .
