How do placeholders work?

[magikaru]

Noob question here.

I understand that named mob's often have placeholders that spawn in their place. If I'm camping one of these, do I need to continuously kill the placeholder for the best chance to spawn the named mob? Or will the named just spawn over the placeholder when it's time?

Wiki on placeholders could use an update on this: https://wiki.project1999.com/Placeholder