N/ui/serverWidget Module
Form.addSubtab()
Method Description: Adds a subtab to a form. In order for your subtab to appear on your form, there must be at least one object assigned to the subtab. Otherwise, the subtab will not appear. If you have less than two subtabs on your form, the subtab will not appear. Instead the fields assigned to the tab will appear at the bottom of the form.
Returns: serverWidget.Tab object
Supported Script Types: SuiteScript 2.0 Suitelet Script Type and SuiteScript 2.0 User Event Script Type (beforeLoad(scriptContext))
Governance: None
Module: N/ui/serverWidget Module
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=Form.addSubtab(options)

// Code Example 1

//Add additional code

//...

var form = serverWidget.createForm({

    title : 'Simple Form'

});

form.addSubtab({

    id : 'subtabid',

    label : 'Subtab'

});

//...

//Add additional code



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_4338820096.html