Yes - Atto it is and we are making great progress. MDL-43841 is the epic issue that tracks all of the sub-tasks (not all of the tasks in that Epic will be done, we need to decide on them individually). http://docs.moodle.org/dev/Atto is the start of our dev docs for Atto - it will be expanded on and improved before release (especially as we are changing the API occasionally).
2 of the major features I worked on last week are
1. a new equation editor that works with the existing filter system and has no requirement for Java (and hence is better for accessibility)
2. a built in accessibility checker - each of the new tools will be designed with accessibility in mind - but there will also be a plugin to do some additional checks like colour contrast, alt text for images, headers for table rows etc.
Future major features
Prototyping Editor 2.7
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