Layer ID is a custom attribute of layer element which specifies a unique ID for the layer. This unique ID is used for finding the layer in the slider when you want to use slider API or layer actions.
The layer ID should be unique inside the slider scope. To specify it you need to add it by data-id
attribute
<div id="masterslider" class="master-slider"> <div class="ms-slide"> <!-- .... --> <div class="ms-layer" data-type="text" data-id="foo"> Text layer content here... </div> <!-- .... --> </div> <!-- .... --> </div>