What is the Danelaw, and should I form it?

[General Götterspeise]

Hi everyone, as the title already tells you, I currently have the option of enacting the Danelaw.
I am currently playing as the petty king of East Seaxe, and I have no idea what the hell the Danelaw is supposed to do.
Would I benefit from introducing it?
Will my enemy (Jarldom of Mercia) even agree to it?
I want to go the usual route of forming England-> Britannia, as this is my first playthrough, would this be a valid option?

[AC Denton]

Well, the description tells you what it is and what you get.
The decision is yours to make.

You will get the Kingdom of Danelaw title.
Your enemy will get the Kingdom of England title.
This doesn't stop you from obviously conquering your enemy, England, and taking said title.

I usually ignore the Danelaw method myself, but I assume the point of it is to strategically split England into two Kingdoms, elevating yourself to one of them (Danelaw).
It will lead to the future decision opportunity of "Formalize the Daneland" too.
Again, up to you. All you're doing it splitting England into 2, becoming ruler of one of them.

[kalanyr]

It's there mostly so you can replicate something that happened historically around the 867 start date if you want (or so one of the AIs in an 867 start in England can be a rat bastard in an amusing way).