FreeCAD sketches

My empirical conclusion, after using intensively FreeCAD Sketcher and Part (Design) modules through the GUI, is that xy is the hard coded default plane for a sketch. The sketch can be reoriented or placed elsewhere in the space, either manually or attaching it to a face. Nevertheless the orientation and placement are properties are not hard coded with the sketch object: more than once I lost the  position I defined for some sketches, probably (this is my guesstimation, I had no time to investigate the matter and create a bug report with a reproducible test case) while recovering the open projects, at new start of FreeCAD after a crash of the tool (it happened often).

Once more, when exporting a sketch in “Flattened svg” format, what is exported is the projection of the sketch on the xy plane: I tried it with a sketch oriented on the yz plane and I exported the shapes “collapsed to the bottom of the sketch”.