PROCESSING "NATIVE_FILTER=(ct in ('%ct%'))"

VALIDATION
    'ct' '^[a-zA-Z-]+$'
    'default_ct' 'a'
END

var wmsSource = new ol.source.TileWMS({
   url: 'http://localhost:5000/cgi-bin/mapserv.exe?map=/ms4w/apps/tutorial/htdocs/essai.map&SERVICE=WMS&VERSION=1.1.1%20&REQUEST=GetCapabilities',
        serverType: 'mapserver',
        params: {'LAYERS': 'layer','ct':"value1,value2",'TILED': true}
  });

http://localhost:5000/cgi-bin/mapserv.exe?map=/ms4w/apps/tutorial/htdocs/essai.map&SERVICE=WMS&VERSION=1.1.1%20&REQUEST=GetCapabilities&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&LAYERS=later&ct=value1%2Cvalue2&TILED=true&WIDTH=256&HEIGHT=256&CRS=EPSG%3A3857&STYLES=&BBOX=-5009377.085697312%2C5009377.085697312%2C-9.313225746154785e-10%2C10018754.171394624