[3.P] What is prereqs were instead HD-based?

[Fitz10019]

...instead of trading debatably worthless feats for a prize I may never achieve because of the campaign length.

... or character death.

I like the idea, but HD5 seems low.

With feat requirements, it's clear that you have to have the feat(s) established before the first level of the PrC. What does HD5 mean? Starting a PrC at 5th level or 6th?