Online javascript editor like inDesign

For a project we're currently trying to create an online WYSIWYG editor which should have the same basic functionality as Adobe's InDesign:

• Adding text frames, and linking text frames together
• Master Pages (with baseline, margins, columns and gutter)
• Basic formatting (font size and styles, alignment)

We're trying to enable users to create simple documents using articles on their news-website as a source. Trough a drag'n'drop interface they should be able to quickly build a simple news-paper-like document. The user's creation should get converted to PDF (trough FPDF library). Therefore the editor should create some sort of html with data-attributes containing properties like width, height, etc. so this data can be converted to a json object to be extracted in PHP and loaded into FDPF. The progress in simple steps:

1. Html WYSIWYG generates preview + html attributes with measurements;
2. Post html attributes trough ajax to server sided;
3. PHP server side extracts json and converts it to FPDF object;
4. User is offered PDF file for download.

I've tried looking at iCloud's Pages, which uses SproutCore (or Ember?) as far as I can see, but I think it would be overkill to use that framework, possibly it won't even have the basic functionality I'm looking for.

Has anybody got any idea's how to get started? What JavaScript framework to use (I've used Prototype, Mootools and jQuery in the past) and where to look for possible examples / similar projects?