code: public static String spellDigit(final Number value)
      {
          int v = value.intValue();
  
          if (v < 0 || v > 9)
              return value.toString();
  
          return context.get().digitStrings(v);
      }
docs: <p>
  For decimal digits [0-9], returns the number spelled out. Otherwise,
  returns the number as string.
  </p>
  
  <table border="0" cellspacing="0" cellpadding="3" width="100%">
  <tr>
  <th class="colFirst">Input</th>
  <th class="colLast">Output</th>
  </tr>
  <tr>
  <td>1</td>
  <td>"one"</td>
  </tr>
  <tr>
  <td>2</td>
  <td>"two"</td>
  </tr>
  <tr>
  <td>10</td>
  <td>"10"</td>
  </tr>
  </table>
  
  @param value
  Decimal digit
  @return String representing the number spelled out