The following instructions were written for the Resource perspective, but they will also work in many other perspectives.
To delete an element, attribute, entity, notation or comment:
You can "undo" the deletion of an item. To do so, right-click any element, attribute, entity, notation, or comment and click Undo Delete. You must do this before you close the editor, otherwise, your items will no longer exist on the system and you will have to recreate them if you want them again.
The DTD editor has a built-in mechanism to handle referential integrity issues. When you delete or rename certain nodes, clean up will automatically occur.