Pick some question tagged harry-potter and voldemort like this: Why didn't the basilisk bite in Chamber of Secrets destroy the Horcrux?
If you open it, the browser tab will be titled
harry potter - Why Didn't the Basilisk Bite in Chamber of Secrets Destroy the Horcrux?
Now the browser tab is titled
voldemort - How Did Harry Become a Horcrux?
What sort of algorithm was used to determine the browser tab's title prefix? Why are some questions prefixed with harry potter and others with voldemort and others with yet another different Harry Potter relatd tag?