#283 Missing images in a sequence

[kirschbombe]

Issue #283
Preview: https://preview.iiif.io/cookbook/0283-missing-image/recipe/0283-missing-image/

[glenrobson]

Cookbook Editors are happy for this to go ahead but would suggest the following changes:

• ID is capitalised in implementation notes but should be lowercase as its a property

Suggest rewritting:
"ID, type, height, width, and items properties. The first two are required by the API for any Canvas, the dimensions tell the viewer to maintain a viewing space of the appropriate size, and the final property ensures the widely used IIIF validator will pass the Manifest."

To something like:

"id, type, height, width, and items properties. The items property is empty in this example. The spec doesn’t require the items property but the IIIF-C validator will fail to validate a canvas without an items property as it differentiates between canvas references found in ranges and canvas found in sequences by the presence of items.

Feel free to re-word the above but it was felt it was slightly clearer on the soft requirment for items in a canvas.

[glenrobson]

OK to make changes requested by TRC:

IIIF/trc#120

Then we can merge.