jQuery.extend

jQuery.extend

Hi
how can i extend a filter so that i can invoke it like:

$('#ka:eq(2)')...;         // This version cause a warning in ff: unknown pseudo class ...
$('#ka').eq(2)...;         // But fortunately i can use the filter this way


when i extend it like this
jQuery.extend(jQuery.expr[":"], {
   random: function(a, i, m, r) {
      return Math.random() < m[3] * 1;
   }
});

i can only:
$('#ka:random(0.5)')...       // which works but also causes a warning in ff

but not
$('#ka').random(0.5)...       // which would not cause a warning

how do i extend it properly?