The navigatable option of the Kendo UI Grid works by handling the keydown event. It checks whether the pressed key is "TAB" and if it is, it looks for the first editable cell. When the cell enters edit mode, the first focusable input element is selected. However, when the user tabs again, the grid searches for the next editable cell.
What I can recommend in order to handle the custom navigation through multiple input elements is that you handle the keydown or keypress jQuery events, prevent the default propagation of the event and handle the focus on your own.
I hope you find this helpful.
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