Last modified: 2013-09-06 09:54:39 UTC
< becomes \u003C > becomes \u003E Example is https://test.wikipedia.org/w/index.php?title=Campaign:wlm-pl&oldid=179050&action=edit Note that the <> still work as they should, just that the next person who edits has no idea wtf they are.
So this is either a bug in the JSON prettyification code, or Code Editor. Will investigate.