Tabbed page, page config and page properties

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:

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

And in the tabbed page I fill those properties:

  - component: oh-tab
      title: MyTitle
      icon: f7:squares_below_rectangle
      page: page:mypage
        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?