Steve, I appreciate the explanation. It is unfortunate that such a detailed explanation be lost in a discussion forum and Internet users have to rely on luck to find it.
I tried to import the graphic xxx_etch_copper_bottom_mirror.svg (generated by Fritzing) for bCNC application (interface Arduino GRBL) but bCNC can not import SVG graphics generated in Fritzing. The bCNC imports graphic SVG generated in Inkscape.
So I tried to import the SVG generated in Fritzing to Inkscape, to be then imported into bCNC, but the SVG graphic that Inkscape imports of Fritzing not have the same properties as an SVG graphic generated in Inkscape itself and therefore the result for import bCNC is the same, it does not work.
I'll keep trying other alternatives and perhaps forget SVG for now and redesign PCBs in Eagle to be imported as DXF in bCNC, that is one of those.