As a paid subscriber, I have access to the professional source code. However, there's a line in the grid.js file that calls .kendoFilterCell(), but I can't find kendoFilterCell in the source files.
The line I'm referring to is in kendo.grid.js on line # 4974 and looks like this:
$('<span/>').attr(kendo.attr('field'), field).appendTo(th).kendoFilterCell(settings);