ᐅ Wall cabinet above backsplash

I am getting our kitchen next week.
I only have some concerns. The wall cabinets rest against the existing tile backsplash below. How will the wall cabinets be mounted to ensure they hang perfectly vertical?

Due to the rail, the cabinets have a 1 cm (0.4 inch) gap from the wall at the top. To compensate for this at the bottom, spacers are nailed in. You can skip these and instead place something of the appropriate thickness between the tiles and the cabinet at the bottom, provided the tile backing is not thicker than 1 cm (0.4 inch).

Well, that is one less worry for me already.
Thank you!

It is actually quite common for the upper cabinets to extend slightly below their bottom edge beyond the tiled backsplash. If they were flush at the top, there would always be a dirt gap, which would be unattractive. Also, it would look odd if the tiled backsplash is not perfectly level.