Purpose:

The Drop down Tags UI Pattern offers multiple choice options to the user when using a drop down search. It's a component available in OS platform.

The objective is to provide a code snippet, with implementation details to make it even easier to follow.

Where it can be used:

Multi-selection is a very integral part for UI design for applications where search plays a key role, e.g. Job portals, Commerce sites etc, 

Usually for longer list on the drop down a multi-selection becomes cumbersome as we loose visibility of selections, but this component has high usability as it displays the selection on top.