dhtmlxGrid - Case Insensitive Sorting

By default the sorting for dhtmlx string is sensitive. How to modifie the javascript function to use Insensitive sorting ?
Or how to use insensitive sorting ?

Here you can find a tutorial with a working example:
docs.dhtmlx.com/doku.php?id=dhtm … ve_sorting

Thank you very much.

The link is dead, can you please explain the adviced approach?