code: void writeToViaString(Writer out, String encoding) throws IOException {
          byte[] bufferToWrite = buffer; // this is always the last buffer to write
          int bufferToWriteLen = index;  // index points to our place in the last buffer
          writeToImpl(out, encoding, bufferToWrite, bufferToWriteLen);
      }
docs: This can <b>ONLY</b> be called if there is only a single buffer to write, instead
  use {@link #writeTo(java.io.Writer, String)}, which auto detects if
  {@link #writeToViaString(java.io.Writer, String)} is to be used or
  {@link #writeToViaSmoosh(java.io.Writer, String)}.
  
  @param out      the JspWriter
  @param encoding the encoding
  @throws IOException