If you simply copy the source code of exactly the same reference and citation, the citation will become duplicated. This template is used to indicate that editors on an article have done this.
The best way to resolve the issue is to use named references. Visual editor can produce named references by using the cite reuse option, or by copying a cite note. In addition, AutoWikiBrowser is able to automatically fix this.
Articles with this tag will appear in Category:Wikipedia references cleanup and Category:All articles with duplicate citations.
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