Recently, we implement a major features in CodeMirror while building Logdown editors.
That's Codemirror Composition Mod.
The original problem in CodeMirror is when users are using IME to input CJK words in edit area, people can't rechoose the word due to keyboard event.
Our team solve this issue by using Composition Event API to bypass keyboard event. If you are interested in implementation detail. Here is the article : 用 Composition Event 改進 CodeMirror 對輸入法的支援
Demo: Logdown editors.