What's the math behind Tesselation Detail in the Sprite Editor and SpriteUtility.GenerateOutline()?

I have a texture and a 2D skinned mesh, from which I'm trying to generate a dilated texture and the correspondingly expanded mesh (keeping the source vertices/triangles intact, only adding a skirt or triangles around the original mesh perimeter).

The undocumented and unexposed (as of Unity 2018.1) method

Code (CSharp):

1. UnityEditor.Sprites.SpriteUtility.GenerateOutline(Texture2D texture, Rect rect, float detail, byte alphaTolerance, bool holeDetection, out Vector2[][] paths)

seems like exactly what I want, but I'm having a hard time figuring out what measure the detail parameter is supposed to represent (average edge length? simplification factor? fractal dimension..? ).

I need to generate the triangle skirt with roughly the same tesselation detail as the source mesh, but I have no idea how to estimate the necessary detail value from the mesh. Any suggestions..?

(This is going to be a part of an art pipeline, so asking artists to write down these numbers isn't really an option.)

 

In the end, I decided to just treat it as a black box optimization problem and successively approximate the necessary level of detail (average edge length, in my case) with a primitive binary search.
Still, knowing the math/logic behind GenerateOutline() would be pretty welcome