1. /* */
         jQuery.tablesorter.addParser({
           id: "mm",
           is: function (s)
               {
                 return false;
               },
           format: function (s)
               {
                return s.tolowercase().replace(/december/g ,12).
                                       replace(/november/g ,11).
                                       replace(/october/g  ,10).
                                       replace(/september/g, 9).
                                       replace(/august/g   , 8).
                                       replace(/july/g     , 7).
                                       replace(/june/g     , 6).
                                       replace(/may/g      , 5).
                                       replace(/april/g    , 4).
                                       replace(/march/g    , 3).
                                       replace(/february/g , 2).
                                       replace(/january/g  , 1);
               },
           type: "numeric"
         });

but for whatever reason, that doesn't seem to work, so right now I'm working around the problem by using a bit of trickery with hidden elements, i.e.

1.  <table id="mnthtable" class="tablesorter">
      <thead class="mnth">
        <tr>
          <th>mMonth
          <th>Days
          <th>Distance
          <th>Time
          <th>Speed
      </thead>
   
      <!--    0              1        2             3           4 -->
      <tbody class="mnth">
        <tr><td>aJanuary   <td>  34 <td> 24,220.5 <td>  221:23<td>109.4
        <tr><td>bFebruary  <td>  43 <td> 29,628.5 <td>  260:54<td>113.6
        <tr><td>cMarch     <td>  32 <td> 23,606.6 <td>  221:30<td>106.6
        <tr><td>dApril     <td>  53 <td> 38,198.1 <td>  356:03<td>107.3
        <tr><td>eMay       <td>  74 <td> 60,218.6 <td>  569:47<td>105.7
        <tr><td>fJune      <td>  96 <td> 66,829.0 <td>  673:18<td> 99.3
        <tr><td>gJuly      <td>  97 <td> 67,300.7 <td>  684:18<td> 98.3
        <tr><td>hAugust    <td> 105 <td> 70,171.3 <td>  677:24<td>103.6
        <tr><td>iSeptember <td> 101 <td> 69,652.2 <td>  666:52<td>104.4
        <tr><td>jOctober   <td>  60 <td> 37,786.7 <td>  353:38<td>106.9
        <tr><td>kNovember  <td>  42 <td> 30,919.4 <td>  288:02<td>107.3
        <tr><td>lDecember  <td>  28 <td> 20,678.1 <td>  194:29<td>106.3
      </tbody>
    </table>
   
   

where the CSS for the table looks like

1. thead.mnth tr th:nth-child(1)::first-letter {
     color: #e8e8e8;
     font-family: monospace;
     font-size: inherit;
   }
   
   tbody.mnth tr td:nth-child(1)::first-letter {
     color: #f8f8f8;
     font-family: monospace;
     font-size: inherit;
   }

which works nicely, but obviously there should be a better way.

Can anyone tell me what I'm doing wrong? The actual page using the table is https://prino.neocities.org/log/summary.html It's the last table on the page.