notes

- pretty
 - align maps as well as arrays

- unit tests and example for cmd/oj

- optimize unmarshal
 - direct parse to struct

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- option to detect duplicate keys or make part of validator
 - change stack to include array and map or maybe just map and nil means array
  - check performance hit
  - check added condition of whether keys should be checked. If too high then copy code
 - or separate stack in func for key maps along with dip code

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- Match a JavaScript regular expression. For example, [?(@.description =~ /cat.*/i)]
- Exists syntax? [?(@.x exists)]