tokens: check for e.Source and not e.OriginalSource , if you have set DropTarget = " True " on the ItemsControl & you have DropOver event attached to the ItemsControl , the event argument e.Source should be ItemsControl .
ner_tags: O O B-Variable O O B-Variable O O O O O B-Code_Block I-Code_Block I-Code_Block I-Code_Block I-Code_Block O O B-Class O O O B-Class O O O O B-Class O O O O B-Variable O O B-Class O