question: synchronized void undo ( RTEditText editor ) { Stack < Operation > undoStack = getUndoStack ( editor ) ; if ( ! undoStack . empty ( ) ) { Stack < Operation > redoStack = getRedoStack ( editor ) ; Operation op = undoStack . pop ( ) ; push ( op , redoStack ) ; op . undo ( editor ) ; while ( ! undoStack . empty ( ) && op . canMerge ( undoStack . peek ( ) ) ) { op = undoStack . pop ( ) ; push ( op , redoStack ) ; op . undo ( editor ) ; } } }
target:  Undo the last operation for a specific rich text editor