tokens: I 'm not sure why you need the DragLeave event but if it 's to grab the selected data the easiest way to get the data is not to hook into DragLeave but to hook into PreviewMouseMove .
ner_tags: O O O O O O O O B-Class O O O O O O O O O O O O O O O O O O O O O O B-Class O O O O B-Class O