Tabbed page, page config and page properties

Setup, Configuration and Use Items & Sitemaps
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When building a tabbed page there is something called “Page Configuration” in the “Configure Tab” window and I’m trying to find out what it is for.
I have a page (chart page) where I have defined properties like for a widget:

config:
  label: MyLabel
  period: D
  props:
    - context: item
      description: Line 1
      label: Item1
      name: item1
      required: false
      type: TEXT

And in the tabbed page I fill those properties:

tabs:
  - component: oh-tab
    config:
      title: MyTitle
      icon: f7:squares_below_rectangle
      page: page:mypage
      pageConfig:
        item1: myitem

This works and so I can add the same chart/page several times with different items to the tabbed page.
And I would have expected to find those properties in the “Page Configuration” but it is empty. So my question is: Is the “Page Configuration” for something else? Do I need to define the properties differently for them to show up?