_:attach_new({type="WGroupWS", switchto=true}):attach_new({type="WTiling", sizepolicy="full", bottom=true})
So your submenu, probably will look like:
defmenu("menuattach", {
menuentry("Float WS", "_:attach_new({type=\"WGroupWS\", switchto=true})"),
menuentry("Tiling WS", "_:attach_new({type=\"WGroupWS\", switchto=true}):attach_new({type=\"WTiling\", sizepolicy=\"full\", bottom=true})"),
})
As I understand there is no more pane workspace.menuentry("Float WS", "_:attach_new({type=\"WGroupWS\", switchto=true})"),
menuentry("Tiling WS", "_:attach_new({type=\"WGroupWS\", switchto=true}):attach_new({type=\"WTiling\", sizepolicy=\"full\", bottom=true})"),
})
P.S. That's true for ion3-20090110