In terms of visual features, the editor is now able to use arbitrary fonts and line heights and properly handles right-to-left scripts. There's also support for multiple gutters which no longer scroll horizontally with the content. The editor also allows widgets to be placed between lines or replace arbitrary pieces of content, which should allow for richer editing functionality. Ranges of text can now marked as read-only or atomic so that the cursor skips over them as if it were a single element. More modular event handling and an improved add-on API make CodeMirror 3.0 more amenable to embedding and extending.
The next version of CodeMirror is now in development. CodeMirror 3.1 will overhaul the first-class document handling which will allow documents to be created without editors and for the editor to switch the currently showing documents.