Get the unit of the SVG surface.
If the surface passed as an argument is not a SVG surface, the function sets the error status to CAIRO_STATUS_SURFACE_TYPE_MISMATCH and returns CAIRO_SVG_UNIT_USER.
a SVG #cairo_surface_t
the SVG unit of the SVG surface.
Get the unit of the SVG surface.
If the surface passed as an argument is not a SVG surface, the function sets the error status to CAIRO_STATUS_SURFACE_TYPE_MISMATCH and returns CAIRO_SVG_UNIT_USER.