How to use arrow keys to adjust numerical values in editable list cells?

[gorjious]

From the ToDo.txt, it seems like this is a feature in the pipeline with some temporary ways to implement it.
Would it be possible to ask for a simple demo of a multi-column list with the ability to adjust editable list cells using arrow keys?

I plan to use it in a Glyphs script. There is a way to apply it to EditText boxes by applying GSSteppingTextField but I can't seem to figure out how to make it work for cells in a list.

Piecing together from some demos, I managed to get this far but still can't get it to work.

from vanilla import *
from GlyphsApp import *

GSSteppingTextField = objc.lookUpClass("GSSteppingTextField")
class RightAlignEditTextList2Cell(vanilla.EditTextList2Cell):
	def __init__(self, *args, **kwargs):
		super().__init__(*args, **kwargs)
		editText = self.editText
		print (editText.nsTextFieldClass)
		textField = editText.nsTextFieldClass
#		textField = GSSteppingTextField
		textField = GSSteppingTextField.alloc().init()

class Test:

    def __init__(self):
        items = [
            dict(left="A", right="1"),
            dict(left="BB", right="10"),
            dict(left="CCC", right="100"),
        ]
        columnDescriptions = [
            dict(
                identifier="left",
                width=75
            ),
            dict(
                identifier="right",
                width=75,
                cellClass=RightAlignEditTextList2Cell,
                editable=True
            )
        ]

        self.w = vanilla.Window((200, 200))
        self.w.l = vanilla.List2(
            (10, 10, -10, -10),
            items,
            columnDescriptions=columnDescriptions
        )
        self.w.open()

Test()