The citation module code looks for multiple comma or semicolon separator characters in the value assigned to |author=, |last=, their aliases, and enumerated equivalents (e.g. |author2=, |last2=, etc.).
This test displays an error message for multiple authors' names in a single parameter, as well as single author names that include a comma-separated list of post-nominals: |author=FC White, RN, MD, Ph.D. To fix these errors in citations: Editors should not simply replace |author= with |authors=.
Pages with this condition are automatically placed in Category:CS1 maint: multiple names: authors list.
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.