additional XML element 'json' for embedding raw JSON

E.g.

<arr>
  <json>[1, 1, 2, 3, 5, 8, 13]</json>
  <str><notline/><![CDATA[
<h1>Sequences!</h1>

<img src="foo.svg">

<p>Fun!</p>
]]></str>
</arr>

is [ [1, 1, 2, 3, 5, 8, 13], "<h1>Sequences!</h1>\n\n<img src=\"foo.svg\">\n\n<p>Fun!</p>\n" ]