If window_name is "window", "pane", "menu", or "macro", and the skin file does not have a control of that name already, the proc will create a new control of that type from scratch.
Unfortunately, this means that winclone() is incapable of creating new windows, menus, panes, or macros if the user has an element by those names.
The default dmf file creates a macro and a menu named "macro" and "menu" by default. Which means 90% of the skins that a library will try to interact with will wind up cloning a menu or a macro set instead of creating a blank one, which is a serious problem.