How we should express which Canvas should be opened when I click on the parent Range?

[giacomomarchioro]

At the moment, in some viewers when you click in a parent Range we can reach the contained Canvases but not the first element of the Range itself.
There is some debate on what should be the expected viewer behaviour when a user click on the parent range:
ProjectMirador/mirador#3521 (comment)
The viewers seems to interpret this inconsistently (see for instance TIFY in https://iiif.io/api/cookbook/recipe/0024-book-4-toc/)

For instance, imagine a Book with this structure:

Chapter 1 (page 6)
Chapter 1 Section 1 (page 8)

This wold results in a manifest with this structure:

Manifest
structures
Range (ToC)
          items
             Range (Chapter 1) (when I click it opens the Canvas list but I can't reach the Canvas of the where the first Chapter begins)
             items
                Canvas 1 (Chapter 1 Section 1) (when I click I go to the Section 1 of Chapter 1 as intended)

From the specs the most plausible solution seems to be using start:

{
  "type": "Range",
  "label": { "en": ["Chapter 1"] },
  "start": {
    "id": "https://example.org/manifest/canvas/page6",
    "type": "Canvas"
  },
  "items": [
    {
      "type": "Range",
      "label": { "en": ["Chapter 1 Section 1"] },
      "items": [
        {
          "id": "https://example.org/manifest/canvas/page8",
          "type": "Canvas"
        }
      ]
    }
  ]
}

I open this issue for discussion before using this on a recipe, and in case I think it would be good to have this on the main Presentation API documentation examples.