This question is a bit more widely applicable than just ArcGIS Online I know, but my current focus is really within the context of webmaps in ArcGIS Online. I'm interested in comments both relating to AGOL and also to the wider use of the web map specification.
The question is two-fold:
Is there any way to include/add extra custom properties to the webmap?
Would doing this break anything - e.g. cause a webmap not to load in the map viewer, or not open in Collector?
Obviously, a webmap is just a JSON spec. I tried editing the JSON using ago assistant. I added a custom property and hit save. It appears to save, and I even can see a success response, but when I reload it, the custom property has disappeared. So something seems to be stripping it out. Meaning I can't even test the second part of my question, as I can't get a custom property to save.
Or is there some property that already exists (e.g. a metadata property of some sort) that allows me to save some custom key-value pairs in them that I can leverage?