// debug: once the `debug` method is called, the layer's value 
// 	of opacity will set to 0.6
// NOTE: make sure the method is called before `set`
Mask.debug()

// create mask for dom element(s)
Mask.set(element1, element2, ... elementN);

// remove the mask over the dom element(s)
Mask.remove(element1, element2, ... elementN);