This is a tracking category.

It is used to build and maintain a list or lists of pages—primarily for the sake of the lists themselves and their use in article and category maintenance. It is not part of the encyclopedia's categorization scheme.

More information:

• This category is hidden on its member pages—unless the corresponding user preference (Appearance → Show hidden categories) is set.
• These categories are used to track, build and organize lists of pages needing "attention en masse" (for example, pages using deprecated syntax), or that may need to be edited at someone's earliest convenience.
• These categories also serve to aggregate members of several lists or subcategories into a larger, more efficient list (discriminated by classifications).
• Typically, tracking categories are automatically populated by templates invoked in pages or by the MediaWiki software (see Special:TrackingCategories for an overview of the latter).

Administrators: Please do not delete this category as empty!

This category may be empty occasionally or even most of the time.

This is a tracking category for {{doi}} that use the Accept-this-as-written markup to indicate that although the given DOI is irregular, it is a valid identifier. Most examples are DOIs that end in periods.

This is not an error category and pages in this category should be "fixed" only if the special markup has been misused (see Help:CS1 errors §Check |doi= value, which describes the only valid use of this parameter).

Articles are listed in this category when a {{doi}} template uses the markup regardless of the validity of the DOI.

Pages with this condition are automatically placed in Category:Ignored DOI errors.