Create a Shiny UI handlerSource:
Historically this function was used in ui.R files to register a user interface with Shiny. It is no longer required as of Shiny 0.10; simply ensure that the last expression to be returned from ui.R is a user interface. This function is kept for backwards compatibility with older applications. It returns the value that is passed to it.
A user interace definition
The user interface definition, without modifications or side effects.