code: @GwtIncompatible("incompatible method")
      public void appendTo(final Appendable appendable) throws IOException {
          if (appendable instanceof Writer) {
              ((Writer) appendable).write(buffer, 0, size);
          } else if (appendable instanceof StringBuilder) {
              ((StringBuilder) appendable).append(buffer, 0, size);
          } else if (appendable instanceof StringBuffer) {
              ((StringBuffer) appendable).append(buffer, 0, size);
          } else if (appendable instanceof CharBuffer) {
              ((CharBuffer) appendable).put(buffer, 0, size);
          } else {
              appendable.append(this);
          }
      }
docs: Appends current contents of this <code>StrBuilder</code> to the
  provided {@link Appendable}.
  <p>
  This method tries to avoid doing any extra copies of contents.
  
  @param appendable  the appendable to append data to
  @throws IOException  if an I/O error occurs
  
  @since 3.4
  @see #readFrom(Readable)