What does this button do? about gtkreactive.jl HOT 5 CLOSED

julia> using GtkReactive, Gtk.ShortNames

julia> (a = button("a")) |> Window |> showall
Gtk.GtkWindowLeaf(name="", parent, width-request=-1, height-request=-1, visible=TRUE, sensitive=TRUE, app-paintable=FALSE, can-focus=FALSE, has-focus=FALSE, is-focus=FALSE, can-default=FALSE, has-default=FALSE, receives-default=FALSE, composite-child=FALSE, style, events=0, no-show-all=FALSE, has-tooltip=FALSE, tooltip-markup=NULL, tooltip-text=NULL, window, opacity=1.000000, double-buffered, halign=GTK_ALIGN_FILL, valign=GTK_ALIGN_FILL, margin-left, margin-right, margin-start=0, margin-end=0, margin-top=0, margin-bottom=0, margin=0, hexpand=FALSE, vexpand=FALSE, hexpand-set=FALSE, vexpand-set=FALSE, expand=FALSE, scale-factor=1, border-width=0, resize-mode, child, type=GTK_WINDOW_TOPLEVEL, title=NULL, role=NULL, resizable=TRUE, modal=FALSE, window-position=GTK_WIN_POS_NONE, default-width=-1, default-height=-1, destroy-with-parent=FALSE, hide-titlebar-when-maximized=FALSE, icon, icon-name=NULL, screen, type-hint=GDK_WINDOW_TYPE_HINT_NORMAL, skip-taskbar-hint=FALSE, skip-pager-hint=FALSE, urgency-hint=FALSE, accept-focus=TRUE, focus-on-map=TRUE, decorated=TRUE, deletable=TRUE, gravity=GDK_GRAVITY_NORTH_WEST, transient-for, attached-to, has-resize-grip, resize-grip-visible, application, is-active=TRUE, has-toplevel-focus=TRUE, startup-id, mnemonics-visible=FALSE, focus-visible=FALSE, is-maximized=FALSE)

julia> x = Signal(1)
Signal{Int64}(1, nactions=0)

julia> y_temp = map(sin, x)
Signal{Float64}(0.8414709848078965, nactions=0)

julia> y = map(_ -> value(y_temp), a)
Signal{Float64}(0.8414709848078965, nactions=0)

julia> push!(x, 7)

julia> y_temp
Signal{Float64}(0.6569865987187891, nactions=0)

julia> y
Signal{Float64}(0.8414709848078965, nactions=0)

# Now go click on that button
julia> y
Signal{Float64}(0.6569865987187891, nactions=0)