Adding a new weighting tag to grapphhopper routing based on gpx tracks

Is there any existing tutorial or documentation decribing how to create an EncodedValue ?
I’ve found some discussions detailling some of the classes to extend here :

I tried to inspire from this discussions, and develop new java classes, but I’m not sure if I’m going the right way.
I created an EncodedValue file, extended the EncodedValueFactory with my new EV, and extend the TagParser class with a CustomTagParser, but it didn’t worked yet