The 'Zivilgesetzbuch' (English: Code of Civil Law) is a unique decision for 
Hesse-Darmstadt.
It is possible to enact if Hesse-Darmstadt has invented Ideological Thought.
It gives 0.05 years (roughly 18 days) with of research points, 5 prestige and all POPs in Hesse-Darmstadt lose 1.0 Militancy. There is no negative parts of the decision. Unless one is in dire need of the 5 prestige, (e.g. By being very close to losing secondary power status) then it is worth to safe this decision until a time, where militancy is dangerously high.