fnAddTr - Microsoft JScript runtime error: Object doesn't support this property or method

I know this is probably obvious, but... what js file do I need to include to get fnAddTr()?

I am calling it like this:

var searchRt = $("#visibletable table").dataTable({/* options */});

$("#searchresults table tr").each(function (idx, elem) {
                    searchRt.fnAddTr($(elem));  // elem is a <tr>, add it to existing table
                });

I am using v1.9.2.

Thanks!
Rich