code: function getCommonBaseLayers(map){
      var osmLayer = L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png', {
          attribution: '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
      });
      var bathymetryLayer = L.tileLayer.wms("http://ows.emodnet-bathymetry.eu/wms", {
          layers: 'emodnet:mean_atlas_land',
          format: 'image/png',
          transparent: true,
          attribution: "EMODnet Bathymetry",
          opacity: 0.8
      });
      var coastlinesLayer = L.tileLayer.wms("http://ows.emodnet-bathymetry.eu/wms", {
          layers: 'coastlines',
          format: 'image/png',
          transparent: true,
          attribution: "EMODnet Bathymetry",
          opacity: 0.8
      });
      var bathymetryGroupLayer = L.layerGroup([bathymetryLayer, coastlinesLayer]);    
      bathymetryGroupLayer.addTo(map);
      return {
          "EMODnet Bathymetry": bathymetryGroupLayer,
          "OSM": osmLayer
      };
  }
docs: /*
  Return common layers used in different examples