code: private void deleteImpl(final int startIndex, final int endIndex, final int len) {
          System.arraycopy(buffer, endIndex, buffer, startIndex, size - endIndex);
          size -= len;
      }
docs: Internal method to delete a range without validation.
  
  @param startIndex  the start index, must be valid
  @param endIndex  the end index (exclusive), must be valid
  @param len  the length, must be valid
  @throws IndexOutOfBoundsException if any index is invalid