It is possible to create a Stacks partial that contains stacks within it (such as a Text or Markdown stack), and to pin the content of these stacks so that their content can be edited outside the partials editor window.
But, is it possible to create a Stacks partial that leave open placeholders for stacks?
For example: is it possible to configure a two-column stack with custom settings (for example, to specify the relative width of the two columns), and to then save it as a partial? And then to add it to a page, and drop in the desired stacks into the two column stack drop-areas?
The purpose of this would be to create pre-configured stacks (for e.g. layout purposes) that can accept whatever stacks that are dropped in them.
SOLUTION: It turns out that a stack drop-area can be pinned/unpinned just like editable text-areas.