Hi,
And in my style the lines-file contained the following rules:
highway=null_null & layer<0 [0x01 resolution 10]
highway=null_null & layer=0 [0x02 resolution 10]
highway=null_null & layer>0 [0x03 resolution 10]
highway=null_null & layer='-1' [0x04 resolution 10]
highway=null_null & layer='0' [0x05 resolution 10]
highway=null_null & layer='1' [0x06 resolution 10]
highway=null_null & layer='+1' [0x07 resolution 10]
highway=null_null [0x08 resolution 10]
highway=null_null & layer='0' [0x05 resolution 10]
highway=null_null & layer=0 [0x02 resolution 10]
highway=null_null & layer='1' [0x06 resolution 10]
highway=null_null & layer='+1' [0x07 resolution 10]
highway=null_null & layer='-1' [0x04 resolution 10]
highway=null_null & layer<0 [0x01 resolution 10]
highway=null_null & layer>0 [0x03 resolution 10]
highway=null_null [0x08 resolution 10]