For those cases where a post 1850 book or encyclopedia does not have a publisher, set |publisher=none to suppress this categorization.
Pages with this condition are automatically placed in Category:CS1 maint: location missing publisher.
To display hidden-by-default error messages: Even with this CSS installed, older pages in Wikipedia's cache may not have been updated to show these error messages even though the page is listed in one of the tracking categories.
After (error and/maintenance) messages are displayed, it might still not be easy to find them in a large article with a lot of citations.
Nota bene: these CSS rules are not obeyed by Navigation popups.