Phillip,

Limiting the rules.....Hmm I'm not sure how you do that. Once you make it recursive you can just keep on embedding and it will parse to its hearts content.
Which then kinda puts the onus on have a smart system to traverse sed data. One the top level of the tree it would be a trivial task to search upper nodes for ones of say type 'array' then search that list for the presence of the correct one.
I'm kinda enjoying this actually, because now I'm a lot more equipped to play with some of my rules after tinkering with this.

Regards Paul