I've just added a new Minibuffer command: "save-node-as-xml". The selected node with its subtree is written to a file as a leo outline using the standard file-save-as dialog.
In the past, I've accomplished this by copying the node, then pasting it into a text editor and saving it from there. Or by creating a new outline and pasting the copied node into it. This is easier. I see this command as especially helpful for those cases where you want to share small examples, for instance by attaching them to a post in this forum.
It's now in the devel branch.