Strange error caused by option addition in an HTML dropdown list
===

This HTML code block, which forms a table with a dropdown list as an element works ok.

    <table border="0" summary="Error Models">
    <tr>
    <th>Ambiguity Resolution Options</th>
    </tr>
    <tr>
    <td>
    Strategy: 
    <select name="strategy">
       <option value="off">OFF</option>
       <option value="float">Float</option>
       <option value="instantaneous">Instantaneous</option>
 
    </select>
    </td>
    </tr>
    </table>

When I try to add a "Fix-and-Hold" option into this dropdown list, as follows:

    <option value="fix-and-hold">Fix-and-Hold</option>

I get an error message, which persists even when i changed the "fix-and-hold" value.

As far as I know, there are no restrictions in the possible values that can assigned in value parameter. So, what causes this error?

I use the [Tryit (W3schools)][1] editor to code HTML for test purposes, as i don't have an HTML framework capable of displaying pages without publishing them at this moment.


  [1]: http://www.w3schools.com