function on_open()
    local worlds = core.get_worlds_list()
    for _, name in ipairs(worlds) do
        document.worlds:add(
            "<container ".. 
                "size='380,46' "..
                "color='#0F1E2DB2' "..
                "hover-color='#162B3399' "..
                "onclick='core.open_world(\""..name.."\")'"..
            ">"..
                "<label pos='8,8'>"..name.."</label>"..
                "<button pos='350,5' "..
                        "color='#00000000' "..
                        "hover-color='#FFFFFF2B' "..
                        "onclick='core.delete_world(\""..name.."\")'>"..
                    "<image src='gui/delete_icon' size='32,32' color='#FFFFFF80'/>"..
                "</button>"..
            "</container>"
        )
    end
end