code: function( queryOptions, callback ) {
  		var _this = this;
  		if ( typeof queryOptions === 'function' ) {
  			callback = queryOptions;
  			this.capabilities( function( err, capabilities ) {
  				if ( err ) {
  					debug( "Error getting layers for server '%s': %j", _this.baseUrl,
  						err.stack );
  					return callback( err );
  				}
  				try {
  					callback( null, capabilities.capability.layer.layer );
  				} catch ( e ) {
  					callback( e );
  				}
  			} );
  		} else if ( typeof callback === 'function' ) {
  			this.capabilities( queryOptions, function( err, capabilities ) {
  				if ( err ) {
  					debug( "Error getting layers for server '%s': %j", _this.baseUrl,
  						err.stack );
  					return callback( err );
  				}
  				callback( null, capabilities.capability.layer.layer );
  			} );
  		}
  	}
docs: Gets the WMS service layers reported in the capabilities as an array
  
  @param {Object} [Optional] queryOptions. Options passed as GET parameters
  @param {Function} callback.
  - {Error} null if nothing bad happened
  - {Array} WMS layers as an array Plain Objects