Checked how syntax highlight is done on bespin. It is done on canvas, and I don't think it can be used in other way, so it is discarded for this.
Had a deeper look at EditArea. Substituted the textarea for editarea, and changed mobwrite to sync with editarea box instead of the original one. Synchronization is working, but highlight fails for texts that changes after sync, but come back when pointing cursor near the errors. Fixing will probably have a high cost, esp. for big texts, should discuss if it worth it.