DB2 Zdoom formats?!

When you start a new level in Doom Builder 2 you need to decide which engine to use. Often it would be one of these: Doom 2, Doom, Heretic, Hexen, Strife, etc. But there is also the option to do 'Zdoom (Doom in Hexen format)', or 'Zdoom (Heretic in Hexen format), etc. The best I can tell, you still use the engine of the first game, but the mechanics of the second game. Is this correct? Can anybody explain this to me in a practical sense, and why anyone might want to use these formats?

becouse the hexen format free you from a lot of boundaries, and you can use the acs scripting to make litterally appen anything you want into your mod, and also you can make cinematics and stuff like that, however you don't need it if you whant to do a vanilla compatibile map.

an excellent example of acs scripting is this wad :

http://www.doomworld.com/idgames/?id=12227

take a look if you are interessed. hope i explained myself :S

Elaborating a bit:

http://zdoom.org/wiki/Map_format

Basically, if you're using Doom Builder 2 and you're making a ZDoom exclusive project, go with UDMF for the most features.

Huh, somehow I missed this while searching around on ZDoom Wiki. Thanks for the link Dragonsbrethren!