Toby Speight wrote:

The above means:
* If the highway has both 'ref' and 'name' tags, give it a name made of
the 'ref' value in an oval box, followed by the 'name' value; else

I understood it in this way, but it doesn't do this. I looked for a lot of primaries and secondaries and all of them are named only by there ref.

Are you using the default style? If you're using your own style, then

Yes I'm usind the default style. I changed nothing.

If you want that (ref but no name), then it's easy to change your lines
style thus:
/--------
| highway=motorway {name '${ref|highway-symbol:hbox} ${name}' }
| highway=trunk {name '${ref|highway-symbol:hbox} ${name}' }
| highway=primary {name '${ref|highway-symbol:box} ${name}' }
\--------

Sorry, I'm confused. Above you told me this is how to combine ref and name.

Can you test it please in Mapsource at the following location?
http://www.openstreetmap.org/?lat=51.5916&lon=6.5342&zoom=14&layers=B000FTF

Holding the mouse pointer over the streets shows me the name of the street like this:
B 57, B 58, K 22, Bönninger Strasse

Create a short routing for testing the routing instructions:
From B57 to B58 it tells me: Turn right to B58 (no street name)
>From B57 to K22 it tells me: Turn left to K22 (no street name)
From B57 to Bönninger Straße tells me: Turn left to Bönninger Straße ( but there is no ref stored in the osm data)

Greetings,
Ralf