That probably is the one you are thinking about. The responses in the thread briefly mention that this would be a good way to make icons that are fully responsive to value even though the tutorial itself doesn’t work through that case.
Recently, @DiegoDF just did a nice job using that framework to make an svg that does just that:
Combining his work with the svg library tutorial would allow you to build an icon set responsive to arbitrary values.
Thinking more broadly, now that the png icons are de-ehpmasized (depreciated?) in the main OH icon server in favor of the svg versions it might be worth thinking about actually making the official icons arbitrary in value.