I've spotted that there are some links within the epub using a format in line with JSON
<a href="{"unit": "U01", "page": 24, "exercise": ["AB1"]}">
the href look like this
{"unit": "U01", "page": 24, "exercise": ["AB1"]}
What are those links? are they described in the epub-3 specification? and how does the reader handle that kind of JSON href references?