```I am trying to figure out how to use `TabbedPan...

# doodle

[Stan]

I am trying to figure out how to use `TabbedPanel`.
<https://nacular.github.io/doodle/docs/ui_components/overview#tabbedpanel>

The Demo code shows `TextVisualizer(textMetrics)` taking a `textMetrics` param, but it takes a `Set<Dimension>?` param instead.

I can pass null instead.  Do I not understand the param's class hierarchy?

Anyway, I pass null, to come to the next issue in the Demo code:

`
override fun invoke(item: View, previous: View?, context: Any) =
        textVisualizer(mapping[item] ?: "Unknown")
`

Error:  "No value passed for parameter 'context'"
What do I use for a context?