MD4 vs MD5

[Marscaleb]

I'm just curious, what did the MD5 format bring to the table that MD4 didn't have?

MD1 to MD2 brought interpolation between frames.
MD2 to MD3 made animations more precise so the vertices didn't wobble.
MD3 to MD4 brought about use of skeletal animations.
But what does MD5 have that MD4 didn't?

I tried googling it but it kept directing me to other formats and things called MD4.

[MFG38]

This is just an educated guess, but I'd imagine MD5 is less restricted when it comes to the number of vertices and animation frames you can have in a model as opposed to MD4. After all, that too has been a significant improvement from one version of MDx to another.