function MergedLayer( config ) {

	// NativeLayer inherits from abstract layer "Layer"

	Layer.call( this, config.userConfig );

	/**
	 * Store handler for line group.
	 *
	 * @type { Object }
	 */

	this.lineGroupHandler = undefined;

	/**
	 * Operator for merge function.
	 * Seven kinds of merge function: add, average, concatenate, dot, maximum, multiply, subtract.
	 *
	 * @type { string }
	 */

	this.operator = undefined;

	/**
	 * Identity whether the layer is merged layer.
	 * The different between native layer and merge layer is that the the merged layer's "isMerged" attribute is true.
	 *
	 * @type { boolean }
	 */

	this.isMerged = true;

	/**
	 * Elements participle in merge function.
	 *
	 * @type { Array }
	 */

	this.mergedElements = [];

	/**
	 * layerType will be set based on operation strategy.
	 * For example: Add3d, Subtract1d, Maximum2d
	 *
	 * @type { String }
	 */

	this.layerType = undefined;

}
Operator for merge function.
Seven kinds of merge function: add, average, concatenate, dot, maximum, multiply, subtract.

@type { string }