When editing a biblio in the basic editor, it is not possible to delete certain tags. It is possible to delete subject tags such as 600, 650, etc. But it is not possible to delete a blank 007 despite the icon for delete tag being present. If leaving a blank tag has no impact, then the delete tag icon should be removed. Otherwise, the delete tag ability should be enabled. It is confusing for it to be present if the tag should not be deleted.