I would like to understand why I have to add First around ContourPlot in the following example to have it working:
I looked at the documentation of ContourPlot which says: "ContourPlot returns Graphics[GraphicsComplex[data]]"
So I guess it means that as Epilog needs to take an object of the same type as First[ContourPlot] to work.
But I find it hard to understand it from the documentation.
In order to be more efficient with looking info on the documentation I would like some help to see where it is written. Indeed the only usefull info I found was that ContourPlot returns a Graphics. But where is it explained that Epilog should eat the first element of a Graphics. Furthermore what type is the first element of Graphics ?
Also, for instance on the Epilog documentation is written:
"is an option for graphics functions that gives a list of graphics primitives to be rendered after the main part of the graphics is rendered" This explain what Epilog returns, but not what it "eats". Does that actually means that Epilog must "eat" list of graphic primitives ?