How to solve Shape Plugin issue?

[dubravat]

Hello, fellows

I would like to beg your help.

I am trying to apply OSM bright styles to OSM data (downloaded from geofabrik) in TileMill.

But when I transferred the code from original files into my project files with extension: *mss I got error on a a stage of application styles for roads_high, bridges and tunnels.

/* ---- Casing ----------------------------------------------- */
#roads_high::outline[zoom>=11][zoom<=20],
#tunnel[render='1_outline'][zoom>=11][zoom<=20],
#bridge[render='1_outline'][zoom>=11][zoom<=20]{
  /* -- colors & styles -- */

I tried to save but the program gave me an output:
Shape Plugin: no attribute 'render' in 'C:\path\to\the\project\luxembourg-latest-free.shp\gis.osm_roads_free_1'. Valid attributes are: osm_id,code,fclass,name,ref,oneway,maxspeed,layer,bridge,tunnel.

What could it be can somebody tell me please? And what is the meaning of 'render' parameter where may I find it?

And I also do not understand what 'stylegroup' stands for?

Thank You