I'm working on defining a content format for e-learning delivered by a mobile app at work at the moment.  We like JSON as a content representation.  The problem with JSON is that it's very flexible, it's difficult to restrict the format. Here are four interesting resources that have helped me

• http://json-schema.org/ - Define a schema for the JSON content format (in JSON itself)
• http://jsonary.com/ - Create an editing interface automatically based off the schema you've defined
• http://www.jsonschema.net/ - Give this some sample JSON and it will give you a schema document (which will require editing, but it's a great jump start)
• http://interior.substance.io/modules/document.html - Substance Document is an open standard for manipulating structured digital documents - I'm expecting to use Substance in rich-text fields in my structured JSON files.

All of these resources are web native, javascript friendly, open-source projects.