'interpolate attribute in a group' doesn't work, documentation for paint_order not as useful as it could be

Traceback (most recent call last):
  File "interp_att_g.py", line 174, in <module>
    InterpAttG().run()
  File "/opt/inkscape_1.0.x/share/inkscape/extensions/inkex/base.py", line 140, in run
    self.save_raw(self.effect())
  File "interp_att_g.py", line 153, in effect
    node.style[inte_att] = str(val)
AttributeError: 'str' object has no attribute 'style'

In addition to that, the doc string for the function contains neither 'z-order' nor 'stacking order', nor an indication about which order is achieved (top -> bottom or bottom -> top), which makes it hard to know that this is the function one needs.

In addition to that the term 'paint-order' is already taken in SVG and means something different (https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/paint-order), so if possible (and as it doesn't work anyway), I would like to ask for a renaming of the function, to, e.g. stacking_order or z_order.

Summary To-Do:

• Update documentation string to mention the search relevant key words and the resulting order
• Rename function to reduce confusion?
• Fix interpolate attribute in group extension

(or is this a Python2/3 issue, perhaps?)