A collection of Document Object Model(DOM) elements which are generated from a HTML is called as jQuery object. It is represented as $( ). The elements which are selected are stored in this object. It is much similar to an Array. The selected element or the DOM node index in the SAP UI5 App can be used in the jQuery object to get the UI5 control instance.
var ui5_control_instance = $($0).control(0) ===> UI5 control instance is retrieved.
The elements in the object are thus accessed through the numeric indices. The property length specifies the total number of elements