gstackwidget: Constructor for a stack of widgets
In gWidgets2: Rewrite of gWidgets API for Simplified GUI Construction

This widget is like a notebook – it holds a stack of pages, but does not provide the tabs to work with. Most methods are inherited from gnotebook's.

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gstackwidget(container = NULL, ..., toolkit = guiToolkit())

.gstackwidget(toolkit, container = NULL, ...)

`container`	A parent container. When a widget is created it can be incorporated into the widget heirarchy by passing in a parent container at construction time. (For some toolkits this is not optional, e.g. gWidgets2tcltk or gWidgets2WWW2.)
`...`	These values are passed to the `add` method of the parent container, and occasionally have been used to sneak in hidden arguments to toolkit implementations.
`toolkit`	Each widget constructor is passed in the toolkit it will use. This is typically done using the default, which will lookup the toolkit through `guiToolkit`.

## Not run: 
w <- gwindow("stack widget", visible=FALSE)
add_page <- function(cont, i) {
  g <- gvbox(container=cont)
  glabel(sprintf("page %s",i), container=g)
  bg <- ggroup(container=g); addSpring(bg)
  lb <- gbutton("Previous", container=bg, handler=function(h,...) {
    svalue(cont) <- max(1, i - 1)
  })
  rb <- gbutton("Next", container=bg, handler=function(h,...) {
    svalue(cont) <- min(i + 1, length(cont))
  })
}
sw <- gstackwidget(cont=w)
sapply(1:5, add_page, cont=sw)
visible(w) <- TRUE

## End(Not run)