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This category lists pages that have cs1|2 templates that use |doi=, where a digital object identifier doi value has been specified but then recognized as inactive. These are collected in Category:CS1 maint: DOI inactive.

This may represent:

• An incorrectly specified DOI. In this case, the DOI in question should be corrected.
• A DOI awaiting entry into the Handle System system. In this case, the DOI will soon be active, and a bot will remove the doi-broken-date parameter next time it checks the transcluding article. The article will be correctly listed in this category but does not require further editing until the DOI becomes active.
• A system error with the DOI resolving agency. This should be reported to the DOI resolver (e.g. Crossref) so that it can be fixed - preferably including a link to the journal article claiming the link as further information.
• Publisher issues. A new publisher may have taken over a journal, or a publisher may not yet support DOIs, despite assigning them. In this case, the DOI may not produce a usable hyperlink but still serves as a permanent identifier for the article in question. It should be marked using the |doi-broken-date= parameter of {{cite xxx}}. The article will then be correctly listed in this category until the DOI becomes active. The DOI error report method might not work for these, since the publisher and the DOI owner are not the same.
• The DOI has changed, such as the Archives of Pathology & Laboratory Medicine which changed its DOIs when it changed publishers.
• Internal use only DOI. The American Medical Association, for example, assigns a DOI to all of its journal articles, but many of these are only in the META tags on the web pages and Crossref will not resolve these. Since these can be found with an Internet search engine and might eventually resolve they should be left in the citation.
• The DOI resolves to a dead link. These are hard to report, since the doi.org thinks the DOI works and sometimes the journal no longer exists.

Pages in this category should only be added by Module:Citation/CS1.

By default, Citation Style 1 and Citation Style 2 error messages are visible to all readers and maintenance messages are hidden from all readers.

To display maintenance messages in the rendered article, include the following text in your common CSS page (common.css) or your specific skin's CSS page and (skin.css).

(Note to new editors: those CSS pages are specific to you, and control your view of pages, by adding to your user account's CSS code. If you have not yet created such a page, then clicking one of the .css links above will yield a page that starts "Wikipedia does not have a user page with this exact name." Click the "Start the User:username/filename page" link, paste the text below, save the page, follow the instructions at the bottom of the new page on bypassing your browser's cache, and finally, in order to see the previously hidden maintenance messages, refresh the page you were editing earlier.)

.mw-parser-output span.cs1-maint {display: inline;} /* display Citation Style 1 maintenance messages */

To display hidden-by-default error messages:

.mw-parser-output span.cs1-hidden-error {display: inline;} /* display hidden Citation Style 1 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. A null edit will resolve that issue.

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. Messages can then be found by searching (with Ctrl-F) for "(help)" or "cs1".

To hide normally-displayed error messages:

.mw-parser-output span.cs1-visible-error {display: none;} /* hide Citation Style 1 error messages */

You can personalize the display of these messages (such as changing the color), but you will need to ask someone who knows CSS or at the technical village pump if you do not understand how.

Nota bene: these CSS rules are not obeyed by Navigation popups. They also do not hide script warning messages in the Preview box that begin with "This is only a preview; your changes have not yet been saved".