From Safer nicotine wiki
The test is:
- Is this page in the Category namespace?
- Does this page's title end in "nn(st|nd|rd|th)-century something"
- does the first linked cat's title end in the same "-century something" as the title of the page it is used on?
If the answer to all 3 is yes, then categorise the page in the hidden tracking category Category:Template Category see also used when Template Category pair probably should be