A console.log(UI) will produce the following result 
Object {_DOMBackend: Object, _EventSupport: Object, _throwNextException: false, currentView: null, _globalHelpers: Object…}
It seems there is a lack of documentation out there, would someone kindly share more information on this?
Thanks in advance.
                        
It's not documented because it's been deprecated a while ago.
UIused to contain several functions that were moved to theTemplatenamespace, ieUI.registerHelperis nowTemplate.registerHelper.You can just ignore it, as it will be eventually removed in future versions of Meteor.