[Gmsh] How to know the elementary entities list created when merging a step file

[NENNIG Benoit]

Dear gmsh team,

I would like to put some "complex" 3D part in a cube, then to mesh the complementary volume (cube - the part), to set Physical groups and to save it automatically.

> the complex 3D shape comes from FreeCAD using step format for instance
> the reminder of the tasks are performed in gmsh geo-script

Everything works fine, I can do what I need at hands, but I need to make it automatically.
To do that, I didn't know how to
- find the boundary surfaces list of an "opencascade" volume, the command boundary seems limited to native gmsh geometrical instances:
Vol2Suf[] = Boundary { Volume{1 };};    // Volume 1 is the step part.
Error   : Impossible to take boundary of entity 1 (of type 402)

OR
- How to get the list of all elementary existing surfaces and volumes in a script, If think it is possible because the menu "visibility" provides this list !

If I get such information I think my problem will be solved ;-)

If it is not possible, perhaps, I can simply count the volume and surface creation keywords in the .step file but if there is some more elegant way, it would be nice ;-)

Thank for your suggestions,

Regards,

Benoit